Impact of obstructive sleep apnoea and intermittent hypoxia on blood rheology: a translational study

Xavier Waltz, Andrew E. Beaudin, Elise Belaidi, Jill Raneri, Jean-Louis Pépin, Vincent Pialoux, Patrick J. Hanly, Samuel Verges, Marc J. Poulin
European Respiratory Journal 2021 58: 2100352; DOI: 10.1183/13993003.00352-2021

Abstract

Background Haemorheological alterations are reported in obstructive sleep apnoea (OSA) and reversed with continuous positive airway pressure (CPAP), observations potentially explained by intermittent hypoxia (IH)-induced oxidative stress. Our objective was to investigate whether IH causes haemorheological alterations via oxidative stress.

Methods Wistar rats were exposed to normoxia (n=7) or IH (n=8) for 14 days. 23 moderate-to-severe OSA patients were assessed at three time-points: baseline, after randomisation to either 2 weeks of nocturnal oxygen (n=13) or no treatment (n=10) and after 1 month of CPAP treatment (n=17). Furthermore, an OSA-free control group (n=13) was assessed at baseline and after time-matched follow-up. We measured haemorheological parameters (haematocrit, blood viscosity, plasma viscosity (rats only), erythrocyte aggregation and deformability (humans only)) and redox balance (superoxide dismutase (SOD), glutathione peroxidase, protein oxidation (advanced oxidation protein products (AOPPs)) and lipid peroxidation (malondialdehyde)). We also tested the haemorheological sensitivity of erythrocytes to reactive oxygen species (ROS) in our human participants using the oxidant t-butyl hydroperoxide (TBHP).

Results In rats, IH increased blood viscosity by increasing haematocrit without altering the haemorheological properties of erythrocytes. IH also reduced SOD activity and increased AOPPs. In humans, baseline haemorheological properties were similar between patients and control participants, and properties were unaltered following oxygen and CPAP, except erythrocyte deformability was reduced following oxygen therapy. Redox balance was comparable between patients and control participants. At baseline, TBHP induced a greater reduction of erythrocyte deformability in patients while CPAP reduced TBHP-induced increase in aggregation strength.

Conclusions IH and OSA per se do not cause haemorheological alterations despite the presence of oxidative stress or higher sensitivity to ROS, respectively.

Abstract

Obstructive sleep apnoea and/or intermittent hypoxia per se are not significantly implicated in haemorheological disturbances https://bit.ly/3seciGd

Introduction

Obstructive sleep apnoea (OSA) is characterised by repetitive apnoeas and hypopnoeas resulting in intermittent hypoxaemia (IH), recurrent arousals and intrathoracic pressure swings during sleep [1], all of which are implicated in the pathogenesis of cardiovascular and cerebrovascular disease in OSA [2–5].

Although the many features of OSA, including IH, intermittent hypercapnia, sleep fragmentation, increased negative intrathoracic pressure and elevated sympathetic nerve activity, likely contribute to the increased risk of vascular disease in OSA, evidence implicates chronic IH exposure as the main mediator [6]. A major pathway through which IH contributes to vascular risk is by increasing oxidative stress [7], which in turn promotes endothelial dysfunction [8]. Another potential mechanism is oxidative stress-induced haemorheological alterations [9–12].

Haemorheology is the study of blood flow properties, including blood viscosity, plasma viscosity, erythrocyte aggregation and erythrocyte deformability [13–17], and their impact on blood flow resistance and tissue oxygenation [16, 18, 19]. In observational studies, untreated OSA patients are reported to have altered blood viscosity and erythrocyte aggregation [20–23], two haemorheological alterations predictive of adverse cardiovascular and cerebrovascular events (unstable angina, myocardial infarction and stroke) [24] and endothelial dysfunction [25]. Importantly, in a nonrandomised intervention, 5 days of continuous positive airway pressure (CPAP) treatment appears to reverse haemorheological alterations in OSA patients [22], potentially through correction of OSA-related IH-induced oxidative stress. However, the relationships between IH, oxidative stress and haemorheological alterations have not been examined in the context of OSA.

Employing a translational study design with both an animal model of IH and newly diagnosed OSA patients, we investigated the extent to which 1) IH causes haemorheological alterations and 2) oxidative stress contributes to haemorheological alterations in OSA. We hypothesised that IH causes haemorheological alterations via oxidative stress. To test this hypothesis, we assessed oxidative stress and blood rheology in rats exposed to IH for 14 days, and we compared the effects of nocturnal oxygen therapy (a treatment that rectifies OSA-related IH, but not sleep fragmentation and intrathoracic negative pressure swings related to apnoeic events) and CPAP treatment (a treatment that corrects IH and ancillary features of OSA) in humans. Finally, we examined the susceptibility of blood rheological properties to reactive oxygen species (ROS) in vitro by treating erythrocytes from OSA patients with an oxidant.

Materials and methods

Additional details are provided in the supplementary material.

Animal model of IH (Grenoble, France; 212 m above sea level)

All animal experiments were performed in Grenoble in 2017 in accordance with the Institute for Laboratory Animal Research “Guide for the Care and Use of Laboratory Animals” and approvals (201603301129626) from the Université Grenoble Alpes Ethical Committee. After randomisation, male Wistar rats were exposed to either normoxia (n=7) or severe IH (n=8) for 14 days (8 h·day−1). IH consisted in 60 s cycles alternating 30 s of hypoxia (5% inspiratory oxygen fraction (FIO2) and 30 s of normoxia (21% FIO2). Normoxic rats were exposed to similar air–air cycles. Next, rats were anaesthetised using intraperitoneal injection of pentobarbital (60 mg·kg−1) and received an intravenous heparin injection before blood draw.

Human experiments (Calgary, AB, Canada; 1103 m above sea level)

Experiments were performed according to the Declaration of Helsinki and approved by the Conjoint Health Research Ethics Board of the University of Calgary (REB15-1153). 23 newly diagnosed patients with moderate-to-severe OSA (oxygen desaturation index (ODI) ≥15 events·h−1 and arterial oxygen saturation (SaO2) <90% for ≥12% of total recording time) and 13 OSA-free control participants were recruited (age 18–66 years) between January 2014 and June 2016. OSA was diagnosed by home sleep apnoea testing (HSAT) (Remmers Sleep Recorder; Sagatech Electronics, Calgary, AB, Canada) [26]. The ODI was calculated by indexing the number of times SaO2 decreases by ≥4% to the total SaO2 recording time. Furthermore, a manual respiratory event index (REI) representing the number of apnoeas–hypopnoeas per hour was determined using only the flow channel. Exclusion criteria included previous stroke, body mass index (BMI) ≥40 kg·m−2, peripheral vascular disease, coronary artery disease, hypertension, nephropathy, diabetes, respiratory disorders, pregnancy, current smoker and taking medications affecting the vasculature. All participants gave written informed consent.

Human experimental protocol

The human experimental protocol is shown in supplementary figure E1. After a familiarisation visit, OSA patients performed visit 1 to determine baseline parameters. Next, patients were randomised into either nocturnal oxygen therapy (OSA O2; n=13) or no treatment (OSA Air; n=10) for 2 weeks before a second experimental visit. After visit 2, all patients received CPAP and underwent visit 3 after ∼4 weeks of adherent treatment (post-CPAP). Treatment adherence was defined as CPAP use for ≥4 h·night−1 for ≥70% of the days over 4 consecutive weeks [27]. Before each visit (baseline, post-oxygen and post-CPAP), patients underwent HSAT. Between visit 2 and visit 3 (post-CPAP), six patients were lost to follow-up.

13 OSA-free (HSAT) control participants age and sex matched with OSA patients were recruited. Each performed familiarisation, baseline and follow-up visits. Follow-up visits were scheduled to correspond approximately with the interval between visit 1 (baseline) and visit 3 (post-CPAP) for OSA patients.

Blood pressure in humans

During visit 1, resting brachial blood pressure (BP755; Omron Healthcare, Burlington, ON, Canada) was measured ≥3 times throughout a 10-min period and then averaged.

Haemorheological and haematological parameters

Nonfasting venous blood samples were drawn and placed in EDTA tubes for haematological and haemorheological measurements within 4 h after blood sampling.

Rats

Haematocrit was measured by microcentrifugation. Blood and plasma viscosity were measured at 25°C using a cone-plate viscometer (MCR 302 with CPE 50 spindle; Anton Paar, Graz, Austria). Blood viscosity was measured at low (2.15 s−1) and high shear rates (1000 s−1) and plasma viscosity at 1000 s−1. Blood viscosity was determined both on native blood and after normalising blood to a haematocrit of 40%.

Humans

Haematocrit was measured using a blood gas analyser (ABL837 FLEX; Radiometer, Brønshøj, Denmark). Blood viscosity was measured at ∼23°C using a cone-plate viscometer (DV2T with CPE40 spindle; Brookfield, Middleboro, MA, USA) at low (45 s−1) and higher shear rates (225 s−1). Erythrocyte deformability was measured at 3 and 30 Pa by ektacytometry (at 37°C) and erythrocyte aggregation by syllectometry at a standardised haematocrit of 40% (at 37°C). The disaggregation threshold was determined using a reiteration procedure (LORRCA MaxSis; RR Mechatronics, Hoorn, The Netherlands) [28]. White blood cell and platelet total counts, haemoglobin concentration, and mean cell volume and mean cell haemoglobin concentration were determined using a haematology analyser (Max M-Retic; Coulter, Fullerton, CA, USA).

Assessment of plasma redox balance in rats and humans

Antioxidant enzymes

We determined plasma superoxide dismutase (SOD) [29] and glutathione peroxidase (GPX) activities, as previously described [30].

Oxidative stress biomarkers

Lipid peroxidation and protein oxidation were assessed by quantifying plasma malondialdehyde (MDA) [31] and advanced oxidation protein product (AOPP) concentrations, respectively, as previously described [32].

Erythrocyte rheological response to ROS in humans

Erythrocytes from OSA patients and control participants were incubated with either 5.4 mmol·L−1 of the oxidant t-butyl hydroperoxide (TBHP) diluted in ethanol (Sigma Aldrich, St Quentin-Fallavier, France) (TBHP condition) or with ethanol alone (sham condition) for 10 min at 23°C [11]. Erythrocytes were then resuspended in autologous plasma at a standard haematocrit of 40% prior to erythrocyte deformability and aggregation measurements.

Statistical analyses

For baseline data, we compared OSA and control participants using either independent t-tests or Mann–Whitney rank sum tests. Furthermore, since OSA may be protective or deleterious with respect to cardiovascular and cerebrovascular disease depending on disease severity [33], patients were also divided into two groups based upon the median ODI, i.e. less severe (ODI <35.4 events·h−1) and more severe (ODI ≥35.4 events·h−1) and compared with control participants. Additional details are provided in the supplementary material. Analyses were performed using SPSS version 23 (IBM, Armonk, NY, USA) and presented as mean±sd. The α-level was set a priori at 0.05.

Results

Impact of IH on haematocrit and blood rheology in rats

Figures 1 and 2 show the effects of IH on haematocrit and blood rheology in rats. IH led to an increase in haematocrit (figure 1a). Plasma viscosity was not affected by IH (figure 1b). Blood viscosity at low (figure 2a) and high (figure 2b) shear rates was increased following IH exposure. However, when measured at a normalised haematocrit of 40%, blood viscosity at both low (figure 2c) and high (figure 2d) shear rates was no longer different between hypoxic and normoxic rats.

FIGURE 1
FIGURE 1

Effects of intermittent hypoxia (IH) on a) haematocrit and b) plasma viscosity in rats. FIO2: inspiratory oxygen fraction. Male Wistar rats were exposed to either 14 days of normoxia (n=7) or IH (n=8). The IH stimulus consisted of 60 s cycles alternating 30 s of hypoxia (hypoxic phase at 5% FIO2) and 30 s of normoxia (normoxic phase at 21% FIO2) for 8 h·day−1. One rat was lost for plasma viscosity measurements in the IH group because of a lack of blood/plasma. ***: p<0.001.

FIGURE 2
FIGURE 2

Effects of intermittent hypoxia (IH) on a, b) native and c, d) normalised blood viscosity in rats: a, c) 2.15 s−1 and b, d) 1000 s−1. FIO2: inspiratory oxygen fraction. Male Wistar rats were exposed to either 14 days of normoxia (n=7) or IH (n=8). The IH stimulus consisted of 60 s cycles alternating 30 s of hypoxia (hypoxic phase at 5% FIO2) and 30 s of normoxia (normoxic phase at 21% FIO2) for 8 h·day−1. One rat was lost for normalised blood viscosity measurements in the IH group because of a lack of blood/plasma. ***: p<0.001.

Impact of IH on redox balance in rats

Severe IH reduced SOD activity and increased AOPPs (figure 3a and c, respectively), but had no effect on GPX activity and MDA (figure 3b and d, respectively).

FIGURE 3
FIGURE 3

Effects of intermittent hypoxia (IH) on redox balance in rats: a) superoxide dismutase (SOD), b) glutathione peroxidase (GPX), c) advanced oxidation protein products (AOPPs) and d) malondialdehyde (MDA). FIO2: inspiratory oxygen fraction. Male Wistar rats were exposed to either 14 days of normoxia (n=7) or IH (n=7). The IH stimulus consisted of 60 s cycles alternating 30 s of hypoxia (hypoxic phase at 5% FIO2) and 30 s of normoxia (normoxic phase at 21% FIO2). *: p<0.05.

Baseline characteristics and parameters in control participants and OSA patients

Baseline participant characteristics are summarised in table 1. Age and sex distribution were similar between control participants and OSA patients, whereas OSA patients had a higher BMI, ODI and REI, and greater nocturnal hypoxaemia compared with control participants. Furthermore, control participants, less severe OSA patients and more severe OSA patients had similar age and sex distributions. The more severe OSA patients had a higher BMI compared with control participants. By design ODI, REI and SaO2 <90% exhibited the following continuum: control participants<less severe OSA patients<more severe OSA patients.

View this table:
TABLE 1

Baseline participant characteristics, haematological and haemorheological parameters

OSA patients had higher diastolic blood pressure compared with control participants and tended to have higher mean arterial blood pressure; these results were driven by the more severe OSA patients who had higher mean and diastolic blood pressures compared with control participants.

There were no differences in baseline haematological and haemorheological parameters between control participants and OSA patients. Similarly, no differences were observed between control participants, less severe OSA and more severe OSA patients.

Impact of oxygen and CPAP therapies on blood rheology in OSA patients

Adherence to oxygen and CPAP therapies is summarised in table 2. The mean duration of nocturnal oxygen therapy was 14.5 days with an average use of 7.2 h·night−1. During the 30 days immediately prior to the final experimental visit, OSA patients used CPAP for >4 h·night−1 on ∼89% of the nights, with an average duration of 6 h·night−1. Both oxygen and CPAP led to a decrease in ODI, REI and time with SaO2 <90%. Oxygen therapy increased mean nocturnal SaO2 to a greater extent than CPAP, but decreased REI to a lesser extent than CPAP.

View this table:
TABLE 2

Adherence to oxygen and continuous positive airway pressure (CPAP) treatments and impact of oxygen and CPAP therapies on obstructive sleep apnoea (OSA) severity

Despite excellent adherence to nocturnal oxygen and CPAP therapy, neither treatment modified blood rheological properties (supplementary figures E2 and E3, respectively). However, oxygen therapy caused a decrease in erythrocyte deformability measured at high shear stress (supplementary figure E2f).

Impact of oxygen and CPAP therapies on redox balance

At baseline, redox balance was similar between OSA patients and control participants (figure 4). Furthermore, neither CPAP (figure 4) nor oxygen therapy (figure 5) altered SOD and GPX activities or AOPP and MDA concentrations.

FIGURE 4
FIGURE 4

Effects of continuous positive airway pressure (CPAP) therapy on redox balance: a) superoxide dismutase (SOD) activity, b) glutathione peroxidase (GPX) activity, c) advanced oxidation protein products (AOPPs) and d) malondialdehyde (MDA). OSA: obstructive sleep apnoea. Control participants: n=13; OSA pre-CPAP: n=17; OSA post-CPAP: n=17.

FIGURE 5
FIGURE 5

Effects of oxygen therapy on redox balance: a) superoxide dismutase (SOD) activity, b) glutathione peroxidase (GPX) activity, c) advanced oxidation protein products (AOPPs) and d) malondialdehyde (MDA). OSA: obstructive sleep apnoea. OSA Air: OSA patients not treated with oxygen (n=10); OSA pre-/post-O2: OSA patients treated with oxygen for 2 weeks (n=13). Two samples for AOPPs (pre- and post-O2 in c) and one sample for MDA (post-O2 in d) were lost for technical reasons.

Erythrocyte rheological susceptibility to ROS at baseline in humans

Human erythrocyte haemorheological susceptibility to ROS at baseline is shown in figure 6. Incubation of erythrocytes with TBHP reduced erythrocyte aggregation (figure 6a), increased erythrocyte aggregation strength (i.e. disaggregation threshold) (figure 6b), and decreased erythrocyte deformability measured at low (figure 6c) and high shear stress (figure 6d). Compared with control participants, TBHP-induced decrease of erythrocyte deformability tended to be greater at low shear stress (p=0.08) and was further exacerbated at higher shear stress in OSA patients (figure 6c and d, respectively).

FIGURE 6
FIGURE 6

Erythrocyte rheological susceptibility to reactive oxygen species (t-butyl hydroperoxide (TBHP) incubation) at baseline: a) aggregation, b) disaggregation threshold, c) deformability at 3 Pa and d) deformability at 30 Pa. OSA: obstructive sleep apnoea. Control participants: n=9; OSA patients: n=13. *: p<0.05; ns: nonsignificant.

Impact of oxygen and CPAP therapies on erythrocyte rheological susceptibility to ROS

The impact of oxygen and CPAP therapies on erythrocyte rheological susceptibility to ROS is shown in supplementary figures E4 and E5, respectively. TBHP-induced increase in the erythrocyte disaggregation threshold in OSA patients was unchanged after oxygen treatment (p=0.13) (supplementary figure E4b) and reduced after CPAP treatment (supplementary figure E5b). TBHP-induced alterations in erythrocyte aggregation and deformability were unchanged following oxygen (supplementary figure E4) and CPAP therapies (supplementary figure E5).

Discussion

In rats, we demonstrated that severe IH increased oxidative stress and blood viscosity. However, IH-induced blood hyperviscosity was driven by an increase in haematocrit without concomitant qualitative erythrocyte haemorheological alterations (i.e. erythrocyte aggregation and deformability). Furthermore, we showed in humans that moderate-to-severe OSA was not associated with either haemorheological abnormalities or oxidative stress. Consequently, oxygen and CPAP treatments had no effect on blood rheology, except that oxygen therapy reduced erythrocyte deformability. Nevertheless, erythrocyte deformability was more sensitive to ROS in OSA patients. Furthermore, CPAP decreased the susceptibility of the erythrocyte aggregation strength to ROS. These results suggest that, although OSA patients had a similar degree of oxidative stress compared with control participants at baseline, erythrocyte haemorheological properties are more impacted by ROS induction in OSA patients.

Effects of IH and OSA on haemorheology

Previous studies have reported that OSA patients have, for a given haematocrit, higher blood viscosity and erythrocyte aggregation [21, 22, 34]. Although speculated to result from chronic IH exposure [22], the question of whether IH per se is capable of producing these haemorheological disturbances had not been investigated until now. By exposing male Wistar rats to either 14 days of normoxia or IH, we found that IH leads to an increase in haematocrit and blood viscosity. Yet, when blood viscosity was measured at a standard haematocrit of 40%, it was no longer different between normoxic and IH groups. At a given haematocrit, blood viscosity assessed at low shear rate is mainly determined by erythrocyte aggregation, whereas at high shear rates it is mainly determined by erythrocyte deformability [35]. This suggests that the IH-induced increase in blood viscosity was driven by the increase in haematocrit and that 14 days of severe IH does not cause alterations in erythrocyte aggregation and deformability.

Next, to interrogate the role of IH on haemorheological alterations in OSA, we compared the effects of nocturnal oxygen (a treatment that rectifies OSA-related IH and not ancillary features since apnoeas still persist) and CPAP (a treatment that corrects IH and ancillary features) therapies on haemorheology, in newly diagnosed OSA patients. In contrast to previous studies [21, 22], we observed no haemorheological alterations in OSA patients prior to treatment of OSA. Moreover, in contrast to our animal model of IH, we observed similar haematocrit levels between OSA patients and control participants. This difference between our animal model and OSA patients likely arose from the more severe IH exposure in the animal model compared with our OSA cohort. Furthermore, corroborating the observations made in our animal model of IH, blood viscosity was not different between OSA and control participants when assessed at a standard haematocrit (i.e. 40%). Another potential explanation for the absence of haemorheological alterations in our OSA patients compared with what has been reported previously [21, 22] is that previous studies recruited OSA patients with comorbidities including hypertension, type 2 diabetes mellitus and coronary artery disease, whereas we recruited only normotensive patients free of overt cardiovascular disease. Hence, IH or OSA may not be the sole cause of haemorheological alterations previously reported.

Since haemorheological properties were unaltered at baseline, both oxygen and CPAP therapies had no major effects on blood rheological parameters, except for a reduction in erythrocyte deformability at high shear stress with oxygen therapy. As oxygen therapy induced a mild degree of hyperoxia compared with CPAP (i.e. 95.5% versus 92.2%) (table 2), it is possible that this greater oxygenation may have increased intra-erythrocytic oxidative stress as a result of greater oxygen availability [36]. Baskurt et al. [9] showed that superoxide anions (i.e. ROS) generated externally have a minor effect on erythrocyte deformability, in contrast to superoxide anions generated internally to erythrocytes. Hence, despite unchanged plasma redox balance as measured in the present study, the reduction of erythrocyte deformability observed may be due to the presence of intra-erythrocytic oxidative stress [9]. Additional research is required to test this hypothesis as intra-erythrocytic oxidative stress was not measured in our study.

Effects of IH and OSA on redox balance

In rats, severe IH caused oxidative stress without affecting erythrocyte deformability and aggregation, demonstrating that chronic IH exposure causes only moderate redox imbalance without affecting haemorheology. Furthermore, we did not observe plasma oxidative stress in moderate-to-severe OSA patients.

Nevertheless, we observed that alterations in erythrocyte deformability induced by the same concentration of ROS in situ were exacerbated in erythrocytes from OSA patients compared with control subjects (figure 6). We propose that OSA patients may have reduced intra-erythrocytic antioxidant capacities and therefore greater susceptibility to oxidative stress-induced changes in erythrocyte deformability. This is clinically relevant since a 17% decrease in erythrocyte deformability increases blood flow resistance by 75% (normal endothelial function) to 225% (endothelial dysfunction) [14].

Erythrocyte oxidation with TBHP caused an increase of erythrocyte aggregation strength and a reduction of erythrocyte aggregation and deformability. After oxygen therapy, despite a numerically lower increase in the erythrocyte aggregation threshold and a lower decrease in erythrocyte deformability, these changes were not significant (supplementary figure E4). The same observations were made after CPAP therapy, except that the susceptibility of the erythrocyte aggregation threshold to ROS was significantly reduced (supplementary figure E5). These results are not explained by any changes in plasma redox balance following oxygen or CPAP therapies. Future studies should investigate the effect of IH on intra-erythrocytic ROS production and intra-erythrocytic antioxidant capacities.

Our study has several methodological limitations. First, although cone-plate viscometers were used to assess blood viscosity in both the animal experiments performed in France and the human experiments performed in Canada, they were not the same models. As such, blood viscosity was assessed using different shear rates within the animal (2.15 and 1000 s−1) and human experiments (45 and 225 s−1). Blood viscosity measured at very low shear rates is more affected by erythrocyte aggregation, whereas blood viscosity measured at high shear rates mainly reflects erythrocyte deformability. Hence, blood viscosity measured in our animal experiments is a better surrogate of erythrocyte aggregation and deformability compared with blood viscosity measured in our human experiments. However, this was compensated by directly measuring erythrocyte aggregation and deformability properties in human experiments. This was not possible in animal experiments performed in France.

Second, erythrocyte deformability is a multifactorial phenomenon that depends on cytoplasmic viscosity, volume-to-surface ratio, membrane elasticity, tank treading motion and erythrocyte deformations due to cellular collisions. In the human experiments, erythrocyte deformability was measured using ektacytometry. Using this method, erythrocytes are resuspended in polyvinylpyrrolidone at a low haematocrit (<1%) far below physiological values (i.e. ∼35–45%). Furthermore, polyvinylpyrrolidone viscosity is about 30 times larger than plasma viscosity. Hence, ektacytometry does not take into account phenomena such as deformations due to cellular collisions.

In summary, this study demonstrates that IH, both in an experimental animal model and in humans with OSA, does not in itself cause haemorheological alterations. Similarly, severe IH-induced oxidative stress does not necessarily cause haemorheological disturbances. Interestingly, despite the absence of baseline differences in plasma oxidative stress, we found that OSA patients were vulnerable to a decrease in erythrocyte deformability when exposed to increased ROS. This finding is relevant for clinical scenarios in which OSA patients might experience a higher level of ROS (e.g. diabetes, obesity, hypertension, early atherosclerosis, etc.). Taken together, our results suggest that haemorheological alterations reported in previous studies may be caused by comorbidities associated with OSA, rather than OSA alone.

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Acknowledgements

We thank the healthy volunteers and OSA patients who participated in this study. We also thank Gwennou Coupier, Thomas Podgorski and Lionel Bureau from the Laboratoire Interdisciplinaire de Physique (LIPhy) (Grenoble University, Grenoble, France) for the provision of a blood viscometer, and Lauren L. Drogos (Laboratory of Human Cerebrovascular Physiology, University of Calgary, Calgary, AB, Canada) for her help with blood rheological data collection. Finally, we thank the staff at the Sleep Centre at Foothills Medical Centre, Healthy Heart Sleep Company, Dream Sleep Respiratory (DRS) services and Rimer Alco North America (RANA) Respiratory Care Group in Calgary for their support in participant recruitment and follow-up throughout the study.

Footnotes

  • This article has supplementary material available from erj.ersjournals.com

  • This article has an editorial commentary: https://doi.org/10.1183/13993003.01169-2021

  • Author contributions: The work outlined in this manuscript was led by a multigroup collaboration of senior team members including P.J. Hanly (OSA), V. Pialoux (oxidative stress), E. Belaidi and J-L. Pépin (IH in rodents), and S. Verges and M.J. Poulin (human integrative physiology and IH). X. Waltz, A.E. Beaudin, P.J. Hanly and M.J. Poulin conceived the experimental design of studies conducted in patients with OSA. E. Belaidi, X. Waltz, J-L. Pépin and S. Verges conceived the experimental design of studies conducted in rodents. Primary supervision for X. Waltz was provided by P.J. Hanly and M.J. Poulin (Calgary) and S. Verges (Grenoble), and primary supervision for A.E. Beaudin was provided by P.J. Hanly and M.J. Poulin. The experiments in patients with OSA were performed by A.E. Beaudin, J. Raneri and X. Waltz. The experiments in rodents were performed by X. Waltz and E. Belaidi. All co-authors contributed to the interpretation of the data. X. Waltz wrote the first draft of the manuscript and other co-authors edited the manuscript.

  • Conflict of interest: X. Waltz has nothing to disclose.

  • Conflict of interest: A.E. Beaudin reports other (scholarships) from the Canadian Institutes of Health Research – Heart and Stroke Foundation of Canada (HSFC), Alberta Innovates – Health Solutions (AIHS), and University of Calgary, during the conduct of the study.

  • Conflict of interest: E. Belaidi has nothing to disclose.

  • Conflict of interest: J. Raneri has nothing to disclose.

  • Conflict of interest: J-L. Pépin reports grants and other (research funds) from Air Liquide Foundation, grants, personal fees and other (research funds) from Agiradom, AstraZeneca, Philips and ResMed, grants and personal fees from Fisher and Paykel, Mutualia and Vitalaire, personal fees from Boehringer Ingelheim, Jazz Pharmaceutical, Night Balance and Sefam, outside the submitted work.

  • Conflict of interest: V. Pialoux has nothing to disclose.

  • Conflict of interest: P.J. Hanly has nothing to disclose.

  • Conflict of interest: S. Verges has nothing to disclose.

  • Conflict of interest: M.J. Poulin has nothing to disclose.

  • Support statement: X. Waltz received support from a Harley N. Hotchkiss Postdoctoral Fellowship (Hotchkiss Brain Institute (HBI)), Alberta Innovates – Health Solutions (AIHS) Postgraduate Fellowship programme, Canadian Institutes of Health Research (CIHR) Postdoctoral Fellowship, European Respiratory Society (ERS) Long-term Fellowship and “Fonds de dotation pour la Recherche en Santé Respiratoire (FRSR)”. A.E. Beaudin was supported by an AIHS Doctoral Fellowship, CIHR – Heart and Stroke Foundation of Canada (HSFC) Focus on Stroke Doctoral Fellowship, William H. Davies Medical Research Scholarship (University of Calgary), and Osten-Victor Graduate Scholarship in Cardiology (University of Calgary). Funding for the human part of the present project was provided by CIHR (PI M.J. Poulin, co-applicant P.J. Hanly) and BRAIN CREATE (an interdisciplinary training programme) funded by the Natural Sciences and Engineering Research Council of Canada (PI M.J. Poulin). Funding for the animal part of the present project was provided by “le fond de dotation AGIR pour les maladies chroniques” (E. Belaidi, S. Verges and J-L. Pépin). The LORRCA MaxSis (haemorheological measurements) was purchased with the HBI donor fund (University of Calgary). M.J. Poulin holds the Brenda Strafford Foundation Chair in Alzheimer Research. Funding information for this article has been deposited with the Crossref Funder Registry.

  • Received February 4, 2021.
  • Accepted April 8, 2021.

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Impact of obstructive sleep apnoea and intermittent hypoxia on blood rheology: a translational study
Xavier Waltz, Andrew E. Beaudin, Elise Belaidi, Jill Raneri, Jean-Louis Pépin, Vincent Pialoux, Patrick J. Hanly, Samuel Verges, Marc J. Poulin
European Respiratory Journal Oct 2021, 58 (4) 2100352; DOI: 10.1183/13993003.00352-2021
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