Training-induced changes on quadriceps muscle oxygenation measured by near-infrared spectroscopy in healthy subjects and in chronic obstructive pulmonary disease patients

AIM

We hypothesize that training-induced changes in muscle oxygen saturation (StO₂ ) assessed by near-infrared spectroscopy (NIRS) during constant work rate cycling exercise (CWRE) may be a useful marker of the effects of training at 'vastus medialis' of the quadriceps in patients with chronic obstructive pulmonary disease (COPD).

METHODS

Incremental exercise [peak oxygen uptake (VO₂ )] and CWRE at 70% pretraining peak VO₂ , before and after 8-w training, were done in 10 healthy age-matched subjects (H) [80% men, 65(11) years, FEV₁ 105(14)%] and 16 COPD patients [94% men, 70(5) years, FEV₁ 46(11) %] encompassing the entire spectrum of disease severity, recruited in the outpatient clinics. NIRS was used to assess StO₂ in the 'vastus medialis' of the left quadriceps.

RESULTS

Pretraining CWRE decreased StO₂ (P<0·05) and generated marked StO₂ rebound (P<0·001) after unloading in the two groups. After training, VO₂ peak increased in H [253(204) ml min^-1 ] (P<0·01) and in COPD [180(183) ml·min^-1 ] (P = 0·01) and blood lactate fell [-4·4 (2·7) and -1·6(2·3) mmol·m^-1 ] (P<0·05 each). Training generated a further fall in StO₂ during CWRE [-10(12)% and -10(10)%, P<0·05] and increased StO₂ rebound after unloading [8(7)% and 5(9)%, P<0·05] in both groups.

CONCLUSION

Endurance training further decreased StO₂ during CWRE, similarly in both groups, likely due to training-induced enhancement of muscle O₂ transfer and utilization. Training-induced StO₂ fall during CWRE may be useful individual marker for non-invasive assessment of enhanced muscle aerobic post-training function.

Postural effects on pulmonary gas exchange abnormalities in severe obesity before and after bariatric surgery

BACKGROUND

We hypothesized that in morbid obesity, pulmonary gas exchange abnormalities will worsen when supine and that bariatric surgery (BS) will mitigate this effect.

METHODS

Gas exchange was investigated in 19 morbidly obese and 8 non-obese, age-matched control females, spontaneously breathing ambient air, both upright and supine, before and one year after BS.

RESULTS

In control non-obese individuals, no postural changes in arterial blood gases (ABGs) were observed. While obese subjects had more altered PaO2, SaO2 and AaPO2 values than controls (P<0.05 each) when upright, the values unexpectedly remained unchanged when supine. This was also the case in the subset of 6 normoxemic obese but the remaining 13 hypoxemic individuals actually improved ABGs when supine: PaO2 (by +2.7±1.3 mmHg, P=0.06), SaO2 (by +1.5±0.6%), pH (by +0.01±0.01) and AaPO2 (by -3.4±1.4 mmHg); and cardiac output increased (by +0.4±0.2 L·min-1) (P<0.05 each). After BS, PaO2 (from 75.5±2.4 to 89.4±2.4 mmHg), AaPO2 (from 27.0±2.0 to 15.4±2.1 mmHg) (P<0.05 each), and pulmonary gas exchange were improved compared to before BS when upright, but ABGs worsened when supine (PaO2, by -4.6±1.7 mmHg; AaPO2, by +4.2±1.6 mmHg) (P<0.05 each).

CONCLUSIONS

Before BS, ABGs are not altered in normoxemic obese subjects moving from upright to supine, even improving in those with hypoxemia when supine. After successful BS, pulmonary gas exchange improved when upright in all subjects but ABGs deteriorated when supine. However, the important clinical observation is the lack of gas exchange deterioration when supine, which may have implications for critical care and anesthesia settings.

Ventilation/Perfusion distribution abnormalities in morbidly obese subjects before and after bariatric surgery

BACKGROUND

Obesity is a global and growing public health problem. Bariatric surgery (BS) is indicated in patients with morbid obesity. To our knowledge, the effects of morbid obesity and BS on ventilation/perfusion (V.a/Q.) ratio distributions using the multiple inert gas elimination technique have never before been explored.

METHODS

We compared respiratory and inert gas (V.a/Q. ratio distributions) pulmonary gas exchange, breathing both ambient air and 100% oxygen, in 19 morbidly obese women (BMI, 45 kg/m2), both before and 1 year after BS, and in eight normal-weight, never smoker, age-matched, healthy women.

RESULTS

Before BS, morbidly obese individuals had reduced arterial Po2 (76 ± 2 mm Hg) and an increased alveolar-arterial Po2 difference (27 ± 2 mm Hg) caused by small amounts of shunt (4.3% ± 1.1% of cardiac output), along with abnormally broadly unimodal blood flow dispersion (0.83 ± 0.06). During 100% oxygen breathing, shunt increased twofold in parallel with a reduction of blood flow to low V.a/Q. units, suggesting the development of reabsorption atelectasis without reversion of hypoxic pulmonary vasoconstriction. After BS, body weight was reduced significantly (BMI, 31 kg/m2), and pulmonary gas exchange abnormalities were decreased.

CONCLUSIONS

Morbid obesity is associated with mild to moderate shunt and V.a/Q. imbalance. These abnormalities are reduced after BS.

Lung function abnormalities are highly frequent in patients with heart failure and preserved ejection fraction

BACKGROUND

Heart failure with preserved ejection fraction (HFPEF) is the most prevalent form of heart failure in outpatients. Yet, the pathophysiology of this syndrome is unclear and pharmacological treatment does not improve prognosis. Because breathlessness during activities of daily living is the most frequent complaint of patients with HFPEF, we hypothesised that lung function may be often abnormal in these patients due to either a direct effect of HFPEF and/or shared risk factors. In this study we explore the frequency, type and severity of lung function abnormalities in HFPEF.

METHODS

We measured forced spirometry, static lung volumes, pulmonary diffusing capacity (DL(CO)) and arterial blood gases in 69 outpatients with newly diagnosed symptomatic HFPEF.

RESULTS

We found that 94% of the patients showed abnormalities in at least one of the lung function measurements obtained: spirometry was abnormal in 59%, DL(CO) in 83% and arterial hypoxaemia was present in 62%. Their severity varied between patients, they were more prevalent in patients with NYHA functional class III/IV, and most often they were undiagnosed and untreated.

CONCLUSIONS

Lung function abnormalities are very frequent in HFPEF patients. A greater awareness among clinicians may contribute to improve their management and health status.

Hemodynamic and gas exchange effects of sildenafil in patients with chronic obstructive pulmonary disease and pulmonary hypertension

RATIONALE

Sildenafil, a phosphodiesterase-5 inhibitor, could be useful for treating pulmonary hypertension (PH) in chronic obstructive pulmonary disease (COPD). However, vasodilators may inhibit hypoxic pulmonary vasoconstriction and impair gas exchange in this condition.

OBJECTIVES

To assess the acute hemodynamic and gas exchange effects of sildenafil in patients with COPD-associated PH.

METHODS

We conducted a randomized, dose comparison trial in 20 patients with COPD-associated PH. Eleven patients were assigned to 20 mg, and 9 patients to 40 mg, of sildenafil. Pulmonary hemodynamics and gas exchange, including ventilation-perfusion (V(A)/Q) relationships, were assessed at rest and during constant-work rate exercise, before and 1 hour after sildenafil administration.

MEASUREMENTS AND MAIN RESULTS

Both sildenafil doses reduced the mean pulmonary arterial pressure (PAP) at rest and during exercise, without differences between them. Overall, PAP decreased -6 mm Hg (95% confidence interval [95% CI], -7 to -4) at rest and -11 mm Hg (95% CI, -14 to -8) during exercise. After sildenafil, Pa(O(2)) decreased -6 mm Hg (95% CI, -8 to -4) at rest because of increased perfusion in units with low V(A)/Q ratio, without differences between doses. No change in Pa(O(2)) (95% CI, -3 to 0.2 mm Hg) or V(A)/Q relationships occurred during exercise after sildenafil. Changes induced by sildenafil in Pa(O(2)) and V(A)/Q distributions at rest correlated with their respective values at baseline.

CONCLUSIONS

In patients with COPD-associated PH, sildenafil improves pulmonary hemodynamics at rest and during exercise. This effect is accompanied by the inhibition of hypoxic vasoconstriction, which impairs arterial oxygenation at rest. The use of sildenafil in COPD should be done cautiously and under close monitoring of blood gases. Clinical trial registered with www.clinicaltrials.gov (NCT00491803).

Effects of nebulized N(G)-nitro-L-arginine methyl ester in patients with hepatopulmonary syndrome

Enhanced pulmonary production of nitric oxide (NO) has been implicated in the pathogenesis of hepatopulmonary syndrome (HPS). NO inhibition with N(G)-nitro-L-arginine methyl ester (L-NAME) in both animals and humans with HPS has improved arterial hypoxemia. We assessed the role of enhanced NO production in the pathobiology of arterial deoxygenation in HPS and the potential therapeutic efficacy of selective pulmonary NO inhibition. We investigated the effects of nebulized L-NAME (162.0 mg) at 30 and 120 minutes on all intrapulmonary and extrapulmonary factors governing pulmonary gas exchange in 10 patients with HPS (60 +/- 7 [SD] yr; alveolar-arterial oxygen gradient, range 19-76 mm Hg; arterial oxygen tension, range 37-89 mm Hg). Nebulized L-NAME maximally decreased exhaled NO (by -55%; P < .001), mixed venous nitrite/nitrate (by -12%; P = .02), and cardiac output (by -11%; P = .002) while increased systemic vascular resistance (by 11%; P = .008) and pulmonary vascular resistance (by 25%; P = .03). In contrast, ventilation-perfusion mismatching, intrapulmonary shunt and, in turn, arterial deoxygenation remained unchanged. In conclusion, gas exchange disturbances in HPS may be related to pulmonary vascular remodeling rather than to an ongoing vasodilator effect of enhanced NO production.

Comparison of manual and automatic CPAP titration in patients with sleep apnea/hypopnea syndrome

Automatic CPAP (auto-CPAP) is engineered to automatically provide a positive pressure to the upper airway in response to apnea, hypopnea, airflow limitation, or snoring in patients with the sleep apnea/ hypopnea syndrome (SAHS). Self-adjusted CPAP has theoretical advantages over traditional fixed CPAP. We investigated the value of auto-CPAP regulation in 20 patients with SAHS in order to predict future fixed-level CPAP needs, as an alternative method to conventional polysomnographically (PSG)-controlled CPAP titration. This was accomplished through comparison of the optimal CPAP level obtained with PSG with that obtained with auto-CPAP. There were no significant differences between the optimal CPAP level achieved with full PSG or with auto-CPAP. As a secondary analysis, we analyzed auto-CPAP performance with regard to sleep-stage distribution and arousals in a group of nine male patients, and compared it with the previous group of 20 patients in which manually CPAP titration was guided by PSG. After adequate CPAP was reached, upward and downward fluctuations in the CPAP level had no significant effect on sleep architecture or fragmentation. We conclude that auto-CPAP permits the prediction of future fixed-level CPAP needs, and does so without sleep disruption.