Examining changes in vascular function, arterial stiffness and systemic inflammation during hospitalization and recovery from an acute exacerbation of chronic obstructive pulmonary disease

An acute exacerbation of COPD (AECOPD) is associated with increased risk of cardiovascular (CV) events. The elevated risk during an AECOPD may be related to changes in vascular function, arterial stiffness, and systemic inflammation; the time course of these measures and their corresponding recovery are poorly understood. Further, physical activity is reduced during an AECOPD, and physical activity may influence the cardiovascular responses to an AECOPD. The purpose of the study was to examine the acute impact of an AECOPD requiring hospitalization on vascular function, arterial stiffness, and systemic inflammation and examine whether physical activity modulates these variables during recovery. Patients hospitalized for an AECOPD were prospectively recruited and compared to control patients with stable COPD. Vascular function, arterial stiffness, and systemic inflammation (CRP, IL-6) were measured at hospital admission, hospital discharge and within 14 days of discharge. Physical activity was electronically tracked daily while in hospital and for 7 days following discharge using a Fitbit. One hundred and twenty-one patients with an AECOPD requiring hospitalization and 33 control patients with stable COPD were enrolled in the study. Vascular function was significantly lower, and systemic inflammation higher at hospital admission in patients with an AECOPD compared to stable COPD. Significant improvements in vascular function and inflammation were observed within 14 days of hospital discharge; however, vascular function remained lower than stable COPD. Physical activity was low at admission and increased following discharge; however, physical activity was unrelated to measures of vascular function or inflammation at any time point. An AECOPD requiring hospitalization is associated with impaired vascular function that persists during recovery. These findings provide a mechanistic link to help explain the enduring increase in CV risk and mortality following a severe AECOPD event.Clinical trial registration: ClinicalTrials.gov #NCT01949727; Registered: 09/20/2013.

Impact of airway challenges on cardiovascular risk in asthma - a randomized controlled trial

BACKGROUND

People experiencing asthma exacerbations are at increased risk of cardiovascular events. To better understand the relationship between asthma exacerbations and cardiovascular risk, this randomized case-control, cross-over controlled trial assessed the immediate systemic inflammatory and vascular responses to acutely induced pulmonary inflammation and bronchoconstriction in people with asthma and controls.

METHODS

Twenty-six people with asthma and 25 controls underwent three airway challenges (placebo, mannitol, and methacholine) in random order. Markers of cardiovascular risk, including serum C-reactive protein, interleukin-6, and tumor necrosis factor, endothelial function (flow-mediated dilation), microvascular function (blood-flow following reactive hyperemia), and arterial stiffness (pulse wave velocity) were evaluated at baseline and within one hour following each challenge. The systemic responses in a) asthma/control and b) positive airway challenges were analyzed. (ClinicalTrials.gov reg# NCT02630511).

RESULTS

Both the mannitol and methacholine challenges resulted in clinically significant reductions in forced expiratory volume in 1 second (FEV1) in asthma (-7.6% and -17.9%, respectively). Following positive challenges, reduction in FEV1 was -27.6% for methacholine and -14.2% for mannitol. No meaningful differences in predictors of cardiovascular risk were observed between airway challenges regardless of bronchoconstrictor response.

CONCLUSION

Neither acutely induced bronchoconstriction nor pulmonary inflammation and bronchoconstriction resulted in meaningful changes in systemic inflammatory or vascular function. These findings question whether the increased cardiovascular risk associated with asthma exacerbations is secondary to acute bronchoconstriction or inflammation, and suggest that other factors need to be further evaluated such as the cardiovascular impacts of short-acting inhaled beta-agonists.

Reliability and validity of the post COVID-19 condition stigma questionnaire: A prospective cohort study

BACKGROUND

Many of the 10-20% percent of COVID-19 survivors who develop Post COVID-19 Condition (PCC, or Long COVID) describe experiences suggestive of stigmatization, a known social determinant of health. Our objective was to develop an instrument, the Post COVID-19 Condition Stigma Questionnaire (PCCSQ), with which to quantify and characterise PCC-related stigma.

METHODS

We conducted a prospective cohort study to assess the reliability and validity of the PCCSQ. Patients referred to our Post COVID-19 Clinic in the Canadian City of Edmonton, Alberta between May 29, 2021 and May 24, 2022 who met inclusion criteria (attending an academic post COVID-19 clinic; age ≥18 years; persistent symptoms and impairment at ≥ 12 weeks since PCR positive acute COVID-19 infection; English-speaking; internet access; consenting) were invited to complete online questionnaires, including the PCCSQ. Analyses were conducted to estimate the instrument's reliability, construct validity, and association with relevant instruments and defined health outcomes.

FINDINGS

Of the 198 patients invited, 145 (73%) met inclusion criteria and completed usable questionnaires. Total Stigma Score (TSS) on the PCCSQ ranged from 40 to 174/200. The mean (SD) was 103.9 (31.3). Cronbach's alpha was 0.97. Test-retest reliability was 0.92. Factor analysis supported a 6-factor latent construct. Subtest reliabilities were >0.75. Individuals reporting increased TSS occurred across all demographic groups. Increased risk categories included women, white ethnicity, and limited educational opportunities. TSS was positively correlated with symptoms, depression, anxiety, loneliness, reduced self-esteem, thoughts of self-harm, post-COVID functional status, frailty, EQ5D5L score, and number of ED visits. It was negatively correlated with perceived social support, 6-min walk distance, and EQ5D5L global rating. Stigma scores were significantly increased among participants reporting employment status as disabled.

INTERPRETATION

Our findings suggested that the PCCSQ is a valid, reliable tool with which to estimate PCC-related stigma. It allows for the identification of patients reporting increased stigma and offers insights into their experiences.

FUNDING

The Edmonton Post COVID-19 Clinic is supported by the University of Alberta and Alberta Health Services. No additional sources of funding were involved in the execution of this research study.

Persistent dyspnea after COVID-19 is not related to cardiopulmonary impairment; a cross-sectional study of persistently dyspneic COVID-19, non-dyspneic COVID-19 and controls

Background: Up to 53% of individuals who had mild COVID-19 experience symptoms for >3-month following infection (Long-CoV). Dyspnea is reported in 60% of Long-CoV cases and may be secondary to impaired exercise capacity (VO_2peak) as a result of pulmonary, pulmonary vascular, or cardiac insult. This study examined whether cardiopulmonary mechanisms could explain exertional dyspnea in Long-CoV.

Methods: A cross-sectional study of participants with Long-CoV (n = 28, age 40 ± 11 years, 214 ± 85 days post-infection) and age- sex- and body mass index-matched COVID-19 naïve controls (Con, n = 24, age 41 ± 12 years) and participants fully recovered from COVID-19 (ns-CoV, n = 14, age 37 ± 9 years, 198 ± 89 days post-infection) was conducted. Participants self-reported symptoms and baseline dyspnea (modified Medical Research Council, mMRC, dyspnea grade), then underwent a comprehensive pulmonary function test, cardiopulmonary exercise test, exercise pulmonary diffusing capacity measurement, and rest and exercise echocardiography.

Results: VO_2peak, pulmonary function and cardiac/pulmonary vascular parameters were not impaired in Long- or ns-CoV compared to normative values (VO_2peak: 106 ± 25 and 107 ± 25%_predicted, respectively) and cardiopulmonary responses to exercise were otherwise normal. When Long-CoV were stratified by clinical dyspnea severity (mMRC = 0 vs mMRC≥1), there were no between-group differences in VO_2peak. During submaximal exercise, dyspnea and ventilation were increased in the mMRC≥1 group, despite normal operating lung volumes, arterial saturation, diffusing capacity and indicators of pulmonary vascular pressures.

Interpretation: Persistent dyspnea after COVID-19 was not associated with overt cardiopulmonary impairment or exercise intolerance. Interventions focusing on dyspnea management may be appropriate for Long-CoV patients who report dyspnea without cardiopulmonary impairment.

COVID-19 hospitalization is associated with pulmonary/diffusion abnormalities but not post-acute sequelae of COVID-19 severity

Coronavirus disease-19 (COVID-19) has resulted in much acute morbidity and mortality worldwide. There is now a growing recognition of the post-acute sequela of COVID-19, termed long COVID. However, the risk factors contributing to this condition remain unclear. Here, we address the growing controversy in the literature of whether hospitalization is a risk factor for long COVID. We found that hospitalization is associated with worse pulmonary restriction and reduction in diffusion capacity at 3 months post-infection. However, the impact on mental health, functional and quality of life is equally severe in those who have and have not been hospitalized during the acute infection. These findings suggest that hospitalization is a risk factor for pulmonary complications of long COVID but not the overall severity of long COVID.

Exertional intolerance and dyspnea with preserved lung function: an emerging long COVID phenotype?

The COVID-19 pandemic has resulted in significant acute morbidity and mortality worldwide. There is now a growing recognition of the longer-term sequelae of this infection, termed "long COVID". However, little is known about this condition. Here, we describe a distinct phenotype seen in a subset of patients with long COVID who have reduced exercise tolerance as measured by the 6 min walk test. They are associated with significant exertional dyspnea, reduced health-related quality of life and poor functional status. However, surprisingly, they do not appear to have any major pulmonary function abnormalities or increased burden of neurologic, musculoskeletal or fatigue symptoms.

Inhaled nitric oxide improves ventilatory efficiency and exercise capacity in patients with mild COPD: A randomized-control cross-over trial

KEY POINTS

Patients with mild chronic obstructive pulmonary disease (COPD) have an elevated ventilatory equivalent to CO₂ production ( V ̇ E / V ̇ C O 2 ) during exercise, secondary to increased dead space ventilation. The reason for the increased dead space is unclear, although pulmonary microvascular dysfunction and the corresponding capillary hypoperfusion is a potential mechanism. Despite emerging evidence that mild COPD is associated with pulmonary microvascular dysfunction, limited research has focused on experimentally modulating the pulmonary microvasculature during exercise in mild COPD. The present study sought to examine the effect of inhaled nitric oxide (iNO), a selective pulmonary vasodilator, on V ̇ E / V ̇ C O 2 , dyspnoea and exercise capacity in patients with mild COPD. Experimental iNO increased peak oxygen uptake in mild COPD, secondary to reduced V ̇ E / V ̇ C O 2 and dyspnoea. This is the first study to demonstrate that experimental manipulation of the pulmonary circulation alone, can positively impact dyspnoea and exercise capacity in mild COPD.

ABSTRACT

Patients with mild chronic obstructive pulmonary disease (COPD) have an exaggerated ventilatory response to exercise, contributing to dyspnoea and exercise intolerance. Previous research in mild COPD has demonstrated an elevated ventilatory equivalent to CO₂ production ( V ̇ E / V ̇ C O 2 ) during exercise, secondary to increased dead space ventilation. The reason for the increased dead space is unclear, although pulmonary microvascular dysfunction and the corresponding capillary hypoperfusion is a potential mechanism. The present study tested the hypothesis that inhaled nitric oxide (iNO), a selective pulmonary vasodilator, would lower V ̇ E / V ̇ C O 2 and dyspnoea, and improve exercise capacity in patients with mild COPD. In this multigroup randomized-control cross-over study, 15 patients with mild COPD (FEV₁  =  89 ± 11% predicted) and 15 healthy controls completed symptom-limited cardiopulmonary exercise tests while breathing normoxic gas or 40 ppm iNO. Compared with placebo, iNO significantly increased peak oxygen uptake (1.80 ± 0.14 vs. 1.53 ± 0.10 L·min^-1 , P < 0.001) in COPD, whereas no effect was observed in controls. At an equivalent work rate of 60 W, iNO reduced V ̇ E / V ̇ C O 2 by 3.8 ± 4.2 units (P = 0.002) and dyspnoea by 1.1 ± 1.2 Borg units (P < 0.001) in COPD, whereas no effect was observed in controls. Operating lung volumes and oxygen saturation were unaffected by iNO in both groups. iNO increased peak oxygen uptake in COPD, secondary to reduced V ̇ E / V ̇ C O 2 and dyspnoea. These data suggest that mild COPD patients demonstrate pulmonary microvascular dysfunction that contributes to increased V ̇ E / V ̇ C O 2 , dyspnoea and exercise intolerance. This is the first study to demonstrate that experimental manipulation of the pulmonary circulation alone, can positively impact dyspnoea and exercise capacity in mild COPD.

The supine position improves but does not normalize the blunted pulmonary capillary blood volume response to exercise in mild COPD

Patients with mild chronic obstructive pulmonary disease (COPD) demonstrate resting pulmonary vascular dysfunction as well as a blunted pulmonary diffusing capacity (DLCO) and pulmonary capillary blood volume (V_C) response to exercise. The transition from the upright to supine position increases central blood volume and perfusion pressure, which may overcome microvascular dysfunction in an otherwise intact alveolar-capillary interface. The present study examined whether the supine position normalized DLCO and V_C responses to exercise in mild COPD. Sixteen mild COPD participants and 13 age-, gender-, and height-matched controls completed DLCO maneuvers at rest and during exercise in the upright and supine position. The multiple FIO2-DLCO method was used to determine DLCO, V_C, and membrane diffusion capacity (D_M). All three variables were adjusted for alveolar volume (DLCOAdj, V_CAdj, and D_MAdj). The supine position reduced alveolar volume similarly in both groups, but oxygen consumption and cardiac output were unaffected. DLCOAdj, D_MAdj, and V_CAdj were all lower in COPD. These same variables all increased with upright and supine exercise in both groups. DLCOAdj was unaffected by the supine position. V_CAdj increased in the supine position similarly in both groups. D_MAdj was reduced in the supine position in both groups. While the supine position increased exercise V_CAdj in COPD, the increase was of similar magnitude to healthy controls; therefore, exercise V_C remained blunted in COPD. The persistent reduction in exercise DLCO and V_C when supine suggests that pulmonary vascular destruction is a contributing factor to the blunted DLCO and V_C response to exercise in mild COPD.NEW & NOTEWORTHY Patients with mild chronic obstructive pulmonary disease demonstrate a combination of reversible pulmonary microvascular dysfunction and irreversible pulmonary microvascular destruction.

The effect of pulmonary rehabilitation on carotid chemoreceptor activity and sensitivity in chronic obstructive pulmonary disease

Recent work demonstrates that carotid chemoreceptor (CC) activity/sensitivity is elevated in patients with chronic obstructive pulmonary disease (COPD) compared with healthy controls, and this elevated chemoreception appears to contribute to increased cardiovascular risk. Exercise training has been shown to normalize CC activity/sensitivity in other populations, and therefore, the purpose of this study was to determine whether pulmonary rehabilitation (PR) can reduce CC activity/sensitivity in COPD. Forty-five COPD patients [mean FEV₁ (forced expiratory volume in 1 s) = 56.6% predicted] completed PR, while 15 COPD patients (mean FEV₁ = 74.6% predicted) served as non-PR controls. CC activity was determined by the reduction in ventilation while breathing transient hyperoxia ([Formula: see text] = 1.0); CC sensitivity was evaluated by the increase in ventilation relative to the drop in arterial saturation while breathing hypoxia. Dyspnea, six-minute walk and autonomic function data were also obtained. PR improved 6-minute walk distance (P < 0.001) and dyspnea (P = 0.04); however, there was no effect on CC activity (P = 0.60), sensitivity (P = 0.69), or autonomic function (P > 0.05 for all). Subgroup analyses indicated that PR reduced CC activity in those with elevated baseline CC activity, independent of changes in autonomic function. No change in dyspnea (P = 0.24), CC activity (P = 0.19), sensitivity (P = 0.80), or autonomic function (P > 0.05 for all) was observed in the control group. Despite improvements in exercise tolerance and dyspnea, PR appears to be generally ineffective at reducing CC sensitivity in stable COPD patients; while PR reduced CC activity in those with elevated basal CC activity, the physiological significance of this is unclear. Further investigations aimed at improving CC function in COPD are needed.NEW & NOTEWORTHY While work in other chronic diseases has shown that exercise training may help normalize carotid chemoreceptor (CC) activity/sensitivity, the current study found that exercise training through pulmonary rehabilitation did not consistently reduce CC activity/sensitivity in patients with chronic obstructive pulmonary disease (COPD). These results suggest that other interventions are needed to normalize CC activity/sensitivity in COPD.

Precapillary pulmonary gas exchange is similar for oxygen and inert gases

KEY POINTS

Precapillary gas exchange for oxygen has been documented in both humans and animals. It has been suggested that, if precapillary gas exchange occurs to a greater extent for inert gases than for oxygen, shunt and its effects on arterial oxygenation may be underestimated by the multiple inert gas elimination technique (MIGET). We evaluated fractional precapillary gas exchange in canines for O2 and two inert gases, sulphur hexafluoride and ethane, by measuring these gases in the proximal pulmonary artery, distal pulmonary artery (1 cm proximal to the wedge position) and systemic artery. Some 12-19% of pulmonary gas exchange occurred within small (1.7 mm in diameter or larger) pulmonary arteries and this was quantitatively similar for oxygen, sulphur hexafluoride and ethane. Under these experimental conditions, this suggests only minor effects of precapillary gas exchange on the magnitude of calculated shunt and the associated effect on pulmonary gas exchange estimated by MIGET.

ABSTRACT

Some pulmonary gas exchange is known to occur proximal to the pulmonary capillary, although the magnitude of this gas exchange is uncertain, and it is unclear whether oxygen and inert gases are similarly affected. This has implications for measuring shunt and associated gas exchange consequences. By measuring respiratory and inert gas levels in the proximal pulmonary artery (P), a distal pulmonary artery 1 cm proximal to the wedge position (using a 5-F catheter) (D) and a systemic artery (A), we evaluated precapillary gas exchange in 27 paired samples from seven anaesthetized, ventilated canines. Fractional precapillary gas exchange (F) was quantified for each gas as F = (P - D)/(P - A). The lowest solubility inert gases, sulphur hexafluoride (SF6 ) and ethane were used because, with higher solubility gases, the P-A difference is sufficiently small that experimental error prevents accurate assessment of F. Distal samples (n = 12) with oxygen (O2 ) saturation values that were (within experimental error) equal to or above systemic arterial values, suggestive of retrograde capillary blood aspiration, were discarded, leaving 15 for analysis. D was significantly lower than P for SF6 (D/P = 88.6 ± 18.1%; P = 0.03) and ethane (D/P = 90.6 ± 16.0%; P = 0.04), indicating partial excretion of inert gas across small pulmonary arteries. Distal pulmonary arterial O2 saturation was significantly higher than proximal (74.1 ± 6.8% vs. 69.0 ± 4.9%; P = 0.03). Fractional precapillary gas exchange was similar for SF6 , ethane and O2 (0.12 ± 0.19, 0.12 ± 0.20 and 0.19 ± 0.26, respectively; P = 0.54). Under these experimental conditions, 12-19% of pulmonary gas exchange occurs within the small pulmonary arteries and the extent is similar between oxygen and inert gases.

Intra-pulmonary arteriovenous anastomoses and pulmonary gas exchange: evaluation by microspheres, contrast echocardiography and inert gas elimination

KEY POINTS

Imaging techniques such as contrast echocardiography suggest that anatomical intra-pulmonary arteriovenous anastomoses (IPAVAs) are present at rest and are recruited to a greater extent in conditions such as exercise. IPAVAs have the potential to act as a shunt, although gas exchange methods have not demonstrated significant shunt in the normal lung. To evaluate this discrepancy, we compared anatomical shunt with 25-µm microspheres to contrast echocardiography, and gas exchange shunt measured by the multiple inert gas elimination technique (MIGET). Intra-pulmonary shunt measured by 25-µm microspheres was not significantly different from gas exchange shunt determined by MIGET, suggesting that MIGET does not underestimate the gas exchange consequences of anatomical shunt. A positive agitated saline contrast echocardiography score was associated with anatomical shunt measured by microspheres. Agitated saline contrast echocardiography had high sensitivity but low specificity to detect a ≥1% anatomical shunt, frequently detecting small shunts inconsequential for gas exchange.

ABSTRACT

The echocardiographic visualization of transpulmonary agitated saline microbubbles suggests that anatomical intra-pulmonary arteriovenous anastomoses are recruited during exercise, in hypoxia, and when cardiac output is increased pharmacologically. However, the multiple inert gas elimination technique (MIGET) shows insignificant right-to-left gas exchange shunt in normal humans and canines. To evaluate this discrepancy, we measured anatomical shunt with 25-µm microspheres and compared the results to contrast echocardiography and MIGET-determined gas exchange shunt in nine anaesthetized, ventilated canines. Data were acquired under the following conditions: (1) at baseline, (2) 2 µg kg-1  min-1 i.v. dopamine, (3) 10 µg kg-1  min-1 i.v. dobutamine, and (4) following creation of an intra-atrial shunt (in four animals). Right to left anatomical shunt was quantified by the number of 25-µm microspheres recovered in systemic arterial blood. Ventilation-perfusion mismatch and gas exchange shunt were quantified by MIGET and cardiac output by direct Fick. Left ventricular contrast scores were assessed by agitated saline bubble counts, and separately by appearance of 25-µm microspheres. Across all conditions, anatomical shunt measured by 25-µm microspheres was not different from gas exchange shunt measured by MIGET (microspheres: 2.3 ± 7.4%; MIGET: 2.6 ± 6.1%, P = 0.64). Saline contrast bubble score was associated with microsphere shunt (ρ = 0.60, P < 0.001). Agitated saline contrast score had high sensitivity (100%) to detect a ≥1% shunt, but low specificity (22-48%). Gas exchange shunt by MIGET does not underestimate anatomical shunt measured using 25-µm microspheres. Contrast echocardiography is extremely sensitive, but not specific, often detecting small anatomical shunts which are inconsequential for gas exchange.

The carotid chemoreceptor contributes to the elevated arterial stiffness and vasoconstrictor outflow in chronic obstructive pulmonary disease

KEY POINTS

The reason(s) for the increased central arterial stiffness in chronic obstructive pulmonary disease (COPD) are not well understood. In this study, we inhibited the carotid chemoreceptor with both low-dose dopamine and hyperoxia, and observed a decrease in central arterial stiffness and muscle sympathetic nervous activity in COPD patients, while no change was observed in age- and risk-matched controls. Carotid chemoreceptor inhibition increased vascular conductance, secondary to reduced arterial blood pressure in COPD patients. Findings from the current study suggest that elevated carotid chemoreceptor activity may contribute to the increased arterial stiffness typically observed in COPD patients.

ABSTRACT

Chronic obstructive pulmonary disease (COPD) patients have increased central arterial stiffness and muscle sympathetic nervous activity (MSNA), both of which contribute to cardiovascular (CV) dysfunction and increased CV risk. Previous work suggests that COPD patients have elevated carotid chemoreceptor (CC) activity/sensitivity, which may contribute to the elevated MSNA and arterial stiffness. Accordingly, the effect of CC inhibition on central arterial stiffness, MSNA and CV function at rest in COPD patients was examined in a randomized placebo-controlled study. Thirteen mild-moderate COPD patients (forced expired volume in 1 s (FEV₁ ) predicted ± SD: 83 ± 18%) and 13 age- and risk-matched controls completed resting CV function measurements with either i.v. saline or i.v. dopamine (2 μg kg^-1  min^-1 ) while breathing normoxic or hyperoxic air (100% O₂ ). On a separate day, a subset of COPD patients and controls completed MSNA measurements while breathing normoxic or hyperoxic air. Arterial stiffness was determined by pulse-wave velocity (PWV) and MSNA was measured by microneurography. Brachial blood flow was determined using Doppler ultrasound, cardiac output was estimated by impedance cardiography, and vascular conductance was calculated as flow/mean arterial pressure (MAP). CC inhibition with dopamine decreased central and peripheral PWV, and MAP (P < 0.05) while increasing vascular conductance in COPD. No change in CV function was observed with dopamine in controls. CC inhibition with hyperoxia decreased peripheral PWV and MSNA (P < 0.05) in COPD, while no change was observed in controls. CC inhibition decreased PWV and MSNA, and improved vascular conductance in COPD, suggesting that tonic CC activity is elevated at rest and contributes to the elevated arterial stiffness in COPD.

Chemosensitivity, Cardiovascular Risk, and the Ventilatory Response to Exercise in COPD

COPD is associated with elevated cardiovascular risk and a potentiated ventilatory response to exercise. Enhanced carotid chemoreceptor (CC) activity/sensitivity is present in other clinical conditions, has been shown to contribute to sympathetic vasoconstrictor outflow, and is predictive of mortality. CC activity/sensitivity, and the resulting functional significance, has not been well examined in COPD. We hypothesized that CC activity/sensitivity would be elevated in COPD, and related to increased pulse wave velocity (a marker of CV risk) and the ventilatory response to exercise.

METHODS

30 COPD patients and 10 healthy age-matched controls were examined. Participants performed baseline cardiopulmonary exercise and pulmonary function testing. CC activity was later evaluated by the drop in ventilation with breathing 100% O2, and CC sensitivity was then assessed by the ventilatory response to hypoxia (ΔVE/ΔSpO2). Peripheral arterial stiffness was subsequently evaluated by measurement of pulse wave velocity (PWV) using applanation tonometry while the subjects were breathing room air, and then following chemoreceptor inhibition by breathing 100% O2 for 2 minutes.

RESULTS

CC activity, CC sensitivity, PWV and the ventilatory response to exercise were all increased in COPD relative to controls. CC sensitivity was related to PWV; however, neither CC activity nor CC sensitivity was related to the ventilatory response to exercise in COPD. CC inhibition by breathing 100% O2 normalized PWV in COPD, while no effect was observed in controls.

CONCLUSION

CC activity and sensitivity are elevated in COPD, and appear related to cardiovascular risk; however, CC activity/sensitivity does not contribute to the potentiated ventilatory response to exercise.

Carotid chemoreceptor modulation of blood flow during exercise in healthy humans

Carotid chemoreceptor (CC) inhibition reduces sympathetic nervous outflow in exercising dogs and humans. We sought to determine if CC suppression increases muscle blood flow in humans during exercise and hypoxia. Healthy subjects (N = 13) were evaluated at rest and during constant-work leg extension exercise while exposed to either normoxia or hypoxia (inspired O(2) tension, F(IO(2)), ≈ 0.12, target arterial O(2) saturation = 85%). Subjects breathed hyperoxic gas (F(IO(2)) ≈ 1.0) and/or received intravenous dopamine to inhibit the CC while femoral arterial blood flow data were obtained continuously with pulsed Doppler ultrasound. Exercise increased heart rate, mean arterial pressure, femoral blood flow and conductance compared to rest. Transient hyperoxia had no significant effect on blood flow at rest, but increased femoral blood flow and conductance transiently during exercise without changing blood pressure. Similarly, dopamine had no effect on steady-state blood flow at rest, but increased femoral blood flow and conductance during exercise. The transient vasodilatory response observed by CC inhibition with hyperoxia during exercise could be blocked with simultaneous CC inhibition with dopamine. Despite evidence of dopamine reducing ventilation during hypoxia, no effect on femoral blood flow, conductance or mean arterial pressure was observed either at rest or during exercise with CC inhibition with dopamine while breathing hypoxia. These findings indicate that the carotid chemoreceptor contributes to skeletal muscle blood flow regulation during normoxic exercise in healthy humans, but that the influence of the CC on blood flow regulation in hypoxia is limited.