Early occurrence of respiratory muscle deoxygenation assessed by near-infrared spectroscopy during leg exercise in patients with chronic heart failure.

The mechanisms of respiratory muscle deoxygenation during incremental leg exercise with expired gas analysis were investigated in 29 patients with chronic heart failure and 21 normal subjects. The deoxygenation and blood volume of the respiratory muscle and exercising leg muscle were assessed by near-infrared spectroscopy (NIRS). To evaluate the influence of the leg exercise on the blood volume of the respiratory muscle, 10 normal subjects also underwent a hyperventilation test with NIRS. The respiratory muscle deoxygenation point (RDP), at which oxygenated hemoglobin starts to decrease, was observed in both groups during exercise. The oxygen consumption (VO2) and the minute ventilation at the RDP in the patients was lower (p<0.01). At the same VO2, the respiratory rate was higher in patients (p<0.01). During exercise, the blood volume of the leg muscle increased, while that of the respiratory muscle decreased. During a hyperventilation test, the minute ventilation was higher than that of the RDP during exercise, the blood volume of the respiratory muscle did not decrease, and the RDP was not detectable. In conclusion, a limited ability to increase perfusion of respiratory muscles during exercise combined with the greater work of breathing results in early respiratory muscle deoxygenation in patients with chronic heart failure.

Skeletal muscle deoxygenation during exercise assessed by near-infrared spectroscopy and its relation to expired gas analysis parameters.

The present study was performed to determine the relation between oxygenated hemoglobin (oxy-Hb) changes in working muscles and ventilatory parameters. Six active normal subjects, 21 sedentary normal subjects and 16 patients with heart failure performed an incremental exercise with expired gas analysis. Deoxygenation of the vastus lateralis muscle was monitored for oxy-Hb changes using near-infrared spectroscopy. Near the anaerobic threshold (AT), oxy-Hb started to decrease, forming the first inflection point (P1). Near the respiratory compensation point (RCP), the second inflection point (P2) was observed. Oxygen uptake at the AT, RCP, P1 and P2 decreased in magnitude first in the active normal subjects, then in sedentary normal subjects and finally in the heart failure patients. High correlation was demonstrated between AT and P1 (r=0.8, p<0.0005) and between RCP and P2 (r=0.9, p<0.0005). In 12 sedentary normal subjects who underwent repeat exercise, reproducibility was confirmed for both P1 and P2. Constant work rate exercises were performed in 5 sedentary normal subjects, and in all of them the oxy-Hb remained unchanged below the AT work rate, whereas oxy-Hb decreased above the AT work rate. Exercise capacity, with respect to both working muscle deoxygenation and ventilation, could be evaluated in detail by the concomitant use of near-infrared spectroscopy and expired gas analysis.

Frequency, significance, and mechanism of myocardial ischemia during daily activities detected by Holter dynamic electrocardiogram.

Exercise testing (EX) and Holter ECG (DCG) were performed consecutively in 52 patients with ischemic heart disease. A total of 100 episodes of myocardial ischemia (IE) were recorded during DCG in 30 patients, who constituted 94% of the patients with myocardial ischemia under 6 metabolic equivalents (METs) during EX. A significant increase in heart rate (HR) was observed before the development of IE. The duration of this increase in HR was longer in IE than in periods in which the HR increased above the ischemic threshold, but without ischemia. The incidence of IE showed two peaks at 8-10 am and 4-6 pm. The frequency of IE among all of the periods with increased HR was highest at 8-10 am (51%). IE in the morning was associated with a lower HR than that in the afternoon, and LF/HF, which reflects sympathetic activity, evaluated using power spectral analysis, increased before IE in the morning. The early appearance of myocardial ischemia in EX can predict its appearance in daily life. The increase in HR and its duration appear to be associated with the development of IE. The increases in sympathetic activity in the morning and the increase in myocardial oxygen demand accompanied by physical activity in the afternoon most likely contributed to the circadian variation in the incidence of ischemic episodes.