Sharmila R. Nabar

A comparison of Qt and a-vO2 in individuals with HIV taking and not taking HAART

PURPOSE The aim of this study was to determine whether highly active antiretroviral therapy (HAART), rather than the direct effect of HIV infection, limits peripheral muscle oxygen extraction-utilization (a-vO(2)) in individuals infected with the human immunodeficiency virus (HIV). METHODS Fifteen subjects (6 female and 9 male) with HIV taking HAART, 15 subjects infected with HIV not taking HAART, and 15 healthy gender and activity level matched non-HIV infected controls (N = 45) performed an maximal treadmill exercise test to exhaustion. Noninvasive cardiac output Qt was measured at each stage and at peak exercise using the indirect Fick method based on the exponential rise carbon dioxide rebreathing method. Intergroup comparisons were adjusted for interactions of peak oxygen consumption ([V02), body surface area, and [V02]t using ANCOVA. RESULTS Peak a-vO(2) was significantly lower (P < 0.05) in subjects with HIV taking HAART (10.0 +/- 0.5 vol%) compared with subjects with HIV not taking HAART (11.7 +/- 0.5 vol%) and noninfected controls (12.7 +/- 0.5 vol%). In subjects with HIV taking HAART, peak heart rate (HR) (170.5 +/- 3.9 bpm) was lower than (P < 0.05) and stroke volume (Vs) (123.0 +/- 3.9 mL x beat-1) at peak exercise was higher (P < 0.05) than subjects with HIV not taking HAART (179.9 +/- 3.5 bpm) (106.6 +/- 3.9 mL x beat-1) and noninfected controls (185.4 +/- 3.8 bpm) (100.6 +/- 4.0 mL.beat-1) upon ANCOVA. There were no significant differences in peak [VO2]t between groups. CONCLUSION Peak a-vO(2) was diminished in subjects infected with HIV taking HAART compared with HIV-infected subjects not taking HAART and noninfected controls matched for age, gender, and physical activity level. Findings of the current study implicated HAART as a primary contributor to decreased muscle oxygen extraction-utilization in individuals infected with HIV.

Decreased peak arteriovenous oxygen difference during treadmill exercise testing in individuals infected with the human immunodeficiency virus

OBJECTIVE To determine if arteriovenous oxygen difference was lower in asymptomatic individuals with human immunodeficiency virus (HIV) infection than in sedentary but otherwise healthy controls. DESIGN Quasi-experimental cross-sectional. SETTING Clinical exercise laboratory. PARTICIPANTS Fifteen subjects (10 men, 5 women) with HIV and 15 healthy gender- and activity level-matched controls (total N=30). INTERVENTION Participants performed an incremental maximal exercise treadmill test to exhaustion. Electrocardiogram, metabolic, and noninvasive cardiac output measurements were evaluated at rest and throughout the tests. Data were analyzed by using analysis of covariance. MAIN OUTCOME MEASURES Peak oxygen consumption (Vo(2)), cardiac output, stroke volume, and arteriovenous oxygen difference. The arteriovenous oxygen difference was determined indirectly using the Fick equation. RESULTS Peak VO(2) was significantly lower (P<.0005) in participants with HIV (24.6+/-1.2mL.kg(-1).min(-1)) compared with controls (32.0+/-1.2mL.kg(-1).min(-1)). There were no significant intergroup differences in cardiac output or stroke volume at peak exercise. Peak arteriovenous oxygen difference was significantly lower (P<.04) in those infected with HIV (10.8+/-0.5 volume %) than in controls (12.4+/-0.5 volume %). CONCLUSION The observed deficit in aerobic capacity in the participants with HIV appeared to be the result of a peripheral tissue oxygen extraction or utilization limitation. In addition to deconditioning, potential mechanisms for this significant attenuation may include HIV infection and inflammation, highly active antiretroviral therapy medication regimens, or a combination of these factors.

Reproducibility of the exponential rise technique of CO2 rebreathing for measuring PvCO2 and CvCO2 to non-invasively estimate cardiac output during incremental, maximal treadmill exercise

The purpose of this study was to determine the reproducibility of the indirect Fick method for the measurement of mixed venous carbon dioxide partial pressure (PvCO2) and venous carbon dioxide content (CvCO2) for estimation of cardiac output (Qc), using the exponential rise method of carbon dioxide rebreathing, during non-steady-state treadmill exercise. Ten healthy participants (eight female and two male) performed three incremental, maximal exercise treadmill tests to exhaustion within 1 week. Non-invasive Qc measurements were evaluated at rest, during each 3-min stage, and at peak exercise, across three identical treadmill tests, using the exponential rise technique for measuring mixed venous PCO2 and CCO2 and estimating venous-arterio carbon dioxide content difference (Cv−aCO2). Measurements were divided into measured or estimated variables [heart rate (HR), oxygen consumption (V̇O2), volume of expired carbon dioxide (V̇CO2), end-tidal carbon dioxide (PETCO2), arterial carbon dioxide partial pressure (PaCO2), venous carbon dioxide partial pressure (PvCO2), and Cv−aCO2] and cardiorespiratory variables derived from the measured variables [Qc, stroke volume (Vs), and arteriovenous oxygen difference (Ca−vO2)]. In general, the derived cardiorespiratory variables demonstrated acceptable (R=0.61) to high (R>0.80) reproducibility, especially at higher intensities and peak exercise. Measured variables, excluding PaCO2 and Cv−aCO2, also demonstrated acceptable (R=0.6 to 0.79) to high reliability. The current study demonstrated acceptable to high reproducibility of the exponential rise indirect Fick method in measurement of mixed venous PCO2 and CCO2 for estimation of Qc during incremental treadmill exercise testing, especially at high-intensity and peak exercise.