Assessing post-exercise respiratory gas kinetics in clinical sample - a pilot study

Funding Acknowledgements

Type of funding sources: None.

Background

Cardiopulmonary exercise testing (CPX) is established in the evaluation of patients with cardiac and pulmonary diseases, and its clinical utility seems to be expanding.  Currently the most important diagnostic and prognostic ventilatory metrics of CPX rely on the exercise phase. Nevertheless, a consistent body of evidence suggests that important information can be derived from the recovery phase, especially in the first few minutes after exercise. In this context, patients with heart failure (HF) demonstrate a slower recovery of the oxygen consumption (VO2) compared with healthy individuals. Purpose: To comprehensively investigate the behavior of respiratory gases during recovery from CPX in a diverse cohort of HF patients. Methods: All individuals who performed CPX at the department of cardiology of Stanford University Hospital were eligible for the study. Patients were included in the experimental group if they (i) were recorded for five minutes after the exercise phase of CPX and (ii) had documented heart failure. They were excluded if they had other clinical diagnoses which may be responsible for exercise intolerance or symptoms or were unable to give informed consent. Healthy controls were recruited from the local community and were included if they did not have documented or suspected disease. Respiratory gases were collected on a breath-by-breath basis and analysed after applying a 30 second rolling average filter. Metrics were analyzed as absolute values, percentage change from peak and the half-time of recovery (T ½; i.e. the duration until a metric had returned to ½ of its value at peak). Data was analyzed over time within patients and averages between groups using parametric statistical methods. In accordance with previous studies, the amount of change in a metric after exercise is presented as the "magnitude" of overshoot. Results: 32 patients with HF (11 Female, 47 ± 13 yrs) and 30 healthy subjects (14 Female, 43 ± 12 yrs) were included. A comparison of ventilatory metrics during recovery between HF and controls is depicted in Figure 1. Peak VO2 was 1135 ± 419 mL/min (13.5 ± 3.8 mL/Kg/min) vs 2408 ± 787 mL/min (32.5 ± 9.0 mL/Kg/min); P <0.01. A significant difference between patients with HF and healthy subjects was found in T ½ of VO2 (111.3 ± 51.0s vs 58.0 ± 13.2s, p < 0.01) and VCO2 (132.0 ± 38.8s vs 74.3 ± 21.1s, p < 0.01). The magnitude of the overshoot was also found to be significantly reduced in patients with HF for VE/VO2 (41.9 ± 29.1% vs 62.1 ± 17.7%, P < 0.01), RQ (25.0 ± 13.6% vs 38.7 ± 15.1%, p < 0.01) and PETO2 (7.2 ± 3.3% vs 10.1 ± 4.6%, p < 0.01). Finally, the magnitude of the RQ overshoot showed a moderate correlation with peak VO2 (ϱ=0.58, p < 0.01). Conclusions: We observed that ventilatory kinetics measured in early recovery after CPX differ significantly between healthy subjects and patients with HF. The assessment of post exercise respiratory gases in a clinical setting may add to the prognostic and diagnostic value of CPX in heart failure.

Abstract Figure.

P4419The association between ECG voltage and left-ventricular mass, sex, body size and the distance between the heart and chest wall in college athletes

Background

The ECG is widely used in pre-participation evaluation (PPE) of athletes (ATH). While it is assumed that greater than normal QRS voltages reflect physiologically increased left ventricular mass (LVM), this has not been adequately demonstrated in ATH.

Purpose

To examine the relation between QRS voltage on surface ECG and LVM and explore if the distance from the chest wall to mid-LV (CWLVdis) affects QRS voltage in ATH.

Methods

We examined digitized ECG data and echocardiograms in college ATH, obtained as part of routine PPE in years 2010–16. ECG parameters included R and S-wave voltage components of the Sokolow-Lyon (S-L) and Cornell criteria for LV hypertrophy (i.e. SV1 + RV5-V6 and RaVL + SV3, respectively). Transthoracic 2D echocardiography was used to determine LVM (area-length method) and the CWLVdis (detailed in Fig1A). S-L positive (SV1 + RV5-V6 >35 mV or RaVL >11 mV) ATH were compared to S-L negative by t-test, and univariate correlation and multivariable regression analysis was used to explore independent effects of body characteristics, sex, LVM and CWLVdis on QRS voltage.

Results

Included were 227 ATH (age 18.6±0.7 yr; 85% male; 60%/33% Caucasian/Afro-american). Of these, 66% played American football, 18% volleyball and 16% basketball.

Overall, mean LVM was 174±37 g (range 96–284 g), and BSA-indexed LVM was 78±12 g/m2 (range 49–108 g/m2). Mean CWLVdis was 8.5±1.1 cm (range 5.6–11.3 cm) and was greater in males (p<0.001, Fig1B).

Forty-six ATH (24%, all male) were S-L positive and no ATH were positive according to Cornell criteria. S-L positive ATH had lower BMI (25.3±3.5 vs 26.9±4.9, p=0.012), greater absolute LVM (189.1±31.3 vs. 170.1±37.4 g, p=0.002) and greater BSA-indexed LVM (85.3±10.3 vs. 76.6±11.7 g/m2, p<0.001) than S-L negative ATH. The CWLVdis was similar between S-L positive and negative ATH (8.4±1.2 vs. 8.6±1.1, respectively, p=0.213).

CWLVdis was more strongly correlated to body mass (r=0.73, p<0.001, Fig. 1C) than to height (r=0.34, p<0.001). LVM correlated weakly to ECG voltage as combined in the S-L or Cornell criteria (Fig. 1C). CWLVdis was weakly correlated with R in aVL, V5 and V6 (r=0.21, 0.16 and 0.16, all p<0.02).

In multivariate analysis, male sex (β=0.31), LVM (β=0.45) and body mass index (β=-0.37) were independently associated with the S-L summed voltage (R2 0.26, p<0.001). For Cornell summed voltage, only sex was an independent predictor (β=0.48, R2 0.22, p<001).

Figure 1

Conclusion

The R and S wave ECG amplitudes used in the two most common ECG criteria for LV hypertrophy were weakly related in the highest to lowest order to sex, LVM, body size and the distance from the LV to the chest wall in our college ATH.