The Time From Anaerobic Threshold (AT) to Respiratory Compensation Point Reflects the Rate of Aerobic and Anaerobic Metabolism After the AT in Chronic Heart Failure Patients

Abstract

hen a subject performs incremental exercising testing, exercise hyperpnea increases toward the end of the exercise. This is due to an increase in acidosis, which is caused by accumulating lactic acid. 1 Lactic acid is produced once the working skeletal muscle cells reach the anaerobic threshold (AT). 2 Usually circulating bicarbonate compensates for this lactic acidosis to begin with. This period is called the isocapnic buffering stage. 3 However, beyond a certain point work intensity becomes so great that lactic acid production can no longer be compensated by circulating bicarbonate and hyperventilation begins. This point is called the respiratory compensation point (RCP). 2 We have previously reported that in heart failure the ability of skeletal muscle to uilize oxygen is increased during mild exercise by increasing the arteriovenous oxygen difference. 4 However, there are few reports of aerobic metabolism after AT. The time from AT to the RCP (RCP-AT time), ie, the duration of isocapnic buffering, varies from subject to subject, although the normal value is believed to be approximately 2 min. 3,5 RCP-AT time depends on the rate of aerobic and anaerobic metabolism after AT, and for subjects with reduced exercise tolerance, such as chronic heart failure patients, this period seems to be shorter. However, the significance of this period is not yet fully understood, and it has not been determined whether the duration of this period is correlated with any indicators of exercise tolerance, such as the anaerobic threshold.Thus, we studied the correlation between the RCP-AT time and the anaerobic threshold and also investigated the correlation between RCP-AT time and the ∆V • O2/∆WR, which is thought to indicate the peripheral blood flow and also the aerobic exercise tolerance. We hypothesized that RCP-AT time may be a new indicator that shows the rate of aerobic and anaerobic metabolism after the AT point. Methods Study PatientsWe studied 37 patients with chronic heart failure (19 men and 18 women); all patients were in New York Heart Association functional class II or III. Their diagnoses were dilated cardiomyopathy and coronary artery disease, and their mean age was 57.8±6.3 years. The nature and the purpose of the study and the risks involved were explained, and informed consent was obtained from each subject before his or her voluntary consent to entry into the study. Ventilatory ParametersPatients performed the cardiopulmonary exercise test under expired gas analysis. Expired gases were monitored continuously in all patients by a breath-by-breath expired gas analyzer (AE280S, Minato Ikagaku, Tokyo, Japan). Oxygen uptake (V • O2), carbon dioxide output (V • CO2), and minute ventilation (V • E) were measured. Anaerobic threshold (AT) was determined as the break point in the V-slope method. 1 The respiratory compensation point (RCP) was determined as the point at which the ratio of minute ventiJpn Circ J 1999; 63: 274 -277 (Received August 5, 1998; revised manuscript received December 24, 1998; accepted December...

The Clinical Significance of Isocapnic Buffering Phase During Exercise Testing: An Overview

“…Since the peak VO 2 represents both central and peripheral cardiopulmonary function, and LVEF only represents central cardiac function, the IB phase may imply the endurance performance in CAD patients derived from peripheral effects regardless of LVEF of patients based on our findings. As ∆VO 2 /∆W slope is an indicator of peripheral blood flow [9,23], the significant correlation between the IB phase and ∆VO 2 /∆W slope revealed in our study also suggests that the IB phase is an indicator of the peripheral cardiopulmonary function. Besides, since the IB phase is associated with the well-recognized prognostic factors such as VE/VCO 2 slope, PetCO 2 at AT and peak VO 2 , the IB phase may also infer prognosis of cardiac disease patients.…”

“…Masaaki Tanehata et al [9] reported that in chronic heart failure patients, the period of IB phase is closely related to the slope of VO 2 as a function of work rate (∆VO 2 /∆WR), but there is no correlation between the RCP-AT time and the anaerobic threshold. They suggested that the RCP-AT time is an indicator of aerobic metabolism after AT.…”

Excessive Ventilatory Response During Exercise in Patients With Non-Hypoxic Pulmonary Hypertension.

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e can evaluate exercise capacity by oxygen consumption (V • O2), carbon dioxide output (V • CO2) and minute ventilation (V • E), [1][2][3][4] and the slope of the linear regression line between V• CO2 and V • E (SLOPE) is a useful parameter for indicating exercise capacity in chronic heart failure patients. [5][6][7][8][9] Furthermore, SLOPE is an index of ventilatory -perfusion inequality.

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“…e can evaluate exercise capacity by oxygen consumption (V • O2), carbon dioxide output (V • CO2) and minute ventilation (V • E), [1][2][3][4] and the slope of the linear regression line between V…”

Effects of Pimobendan on Adverse Cardiac Events and Physical Activities in Patients With Mild to Moderate Chronic Heart Failure

“…Because the symptoms are usually accentuated during exertion, it has been suggested that the functional status of patients with CHF could be reliably indicated by exercise capacity. [26][27][28] However, daily activities do not demand a maximal energy expenditure. Several clinical trials of CHF have included the 'Living With Heart Failure' questionnaire as a measure of QOL.…”