The use of a self-paced cardiopulmonary exercise test in the pre and post-operative care of patients with cardiovascular disease

The aim of this thesis was to assess the ability of a self-paced (SPV) cardiopulmonary exercise test (CPET) in assessing patient fitness prior to elective surgery, and its ability to predict postoperative outcomes. The SPV is a 10 minute test which is comprised of 5 × 2 minute stages. Each stage is fixed to a level on the ratings of perceived exertion (RPE) scale, in an incremental format (RPE: 11, 13, 15, 17 and 20). This test eliminates the need of practitioners having to choose the most appropriate work rate increments to ensure a patient reaches volitional exhaustion within the recommended time period (8-12 min).

Study 1 aimed to assess the reliability of the maximal exercise test parameters obtained from the SPV. Twenty-five (12 females, 13 males) healthy participants completed three SPV tests on three separate occasions. Results demonstrated a coefficient of variation (CV) for V?O2peak (ml·kg-1·min-1) of 4.2% (95% CI: 3.4-5.6%) for trials 2-1, and 5.1% (95% CI: 4.2-6.8%) for trials 3-2. Repeated measures ANOVA analysis demonstrated no significant difference in V?O2peak across the repeated tests (p > 0.05). The limits of agreement (LOA) were ± 5.59 ml·kg-1·min-1 for trials 2-1, and ± 5.86 ml·kg-1·min-1 for trials 3-2. The mean intraclass correlation coefficient (ICC) was 0.95, which represents good reproducibility. It was concluded that the SPV is a reliable indicator of the main CPET derived variables in a healthy population, with comparable values to previous work on standard CPET protocols.

Study 2 investigated the physiological responses between the SPV and a standard CPET (sCPET) protocol between a young (18-30 years) and a middle aged to older adult (50-75 years) population. This was in the attempt to gain an understanding of the response to the protocol and whether these responses differ with age. Expired gases, Q, SV, muscular deoxyhaemoglobin (deoxyHb) and electromyography (EMG) at the vastus lateralis were recorded throughout both tests. Results demonstrated a significantly higher V?O2max in the SPV (49.68 ± 10.26 ml·kg-1·min-1) vs. a sCPET (47.70 ± 9.98 ml·kg-1·min-1) in the young, but no differences in the middle aged to older adult group (> 0.05). Q and SV were significantly higher in the SPV vs. a sCPET in the young (< 0.05) but no differences in the middle aged to older adult group (> 0.05). No differences were seen in both age groups in the deoxyHb and EMG response (> 0.05). Findings from this study suggest that in the young group, the SPV produces higher V?O2max values as a result of an increase in oxygen delivery (enhanced Q). However, likely due to age-related differences, particularly in the cardiovascular response to exercise, the middle aged to older adult group achieved similar V?O2max values regardless of them reaching a higher physiological workload.

Study 3 aimed to assess the validity and reliability of the SPV in post myocardial infarction (post-MI) patients, this was the first study to assess the use of the SPV in a clinical population. Twenty-eight post-MI patients completed one sCPET and two SPVs in a randomised, counterbalanced crossover design. Each patient completed one sCPET and two SPVs. Results demonstrated the SPV to have a coefficient of variation for V?O2peak of 8.2%. The limits of agreement were ± 4.22 ml·kg-1·min-1, with intraclass correlation coefficient of 0.89. There was a significantly higher V?O2peak achieved in the SPV (23.07 ± 4.90 ml·kg-1·min-1) against the sCPET (21.29 ± 4.93 ml·kg-1·min-1). It was concluded that the SPV is a safe and valid test of exercise capacity in post-MI patients, with acceptable levels of reliability when compared to previous work on sCPET protocols.

Study 4 aimed to determine if the SPV can assess patient's preoperative risk similar to sCPET and if exercise variables obtained from the test can accurately predict post-operative outcome. Fifty patients with cardiovascular related co-morbidities completed one sCPET and one SPV, although only thirty of those patients when ahead with surgery. Post-surgery, patients were monitored for incidence of morbidity on postoperative days 3 and 5, length of hospital stay, and incidence of mortality in the 30 days after surgery. Patients achieved a significantly higher V?O2peak, HR, V?E, peak PO and TTE in the SPV compared to the sCPET (P < 0.05). Logistic regression analysis demonstrated that for the thirty patients who had surgery, none of the CPET variables were associated with postoperative morbidity at either day 3 or 5 (P > 0.05). Although when combining postoperative morbidity at days 3 and 5, logistic regression analysis showed that oxygen pulse at AT obtained from the SPV was significantly related to postoperative complications (P < 0.05). ROC curve analysis demonstrated oxygen pulse at AT to provide an AUC of 0.72 a.u. (95%CI 0.51 to 0.92), with an optimal cut-off point of 8.5 ml/beat-1 which provided 72.7% sensitivity and 71.4% specificity. It was concluded that the SPV was able to assess preoperative fitness comparable to the sCPET. Although none of the CPET variable from either test were associated with postoperative morbidity, which is likely a result of the small sample size.

The conclusion for this thesis is that a self-paced CPET test is able to reliably assess cardiovascular patient's fitness comparable to traditional methods. This type of test may be seen as advantageous, this is because the SPV takes away the need of clinicians having to choose the most appropriate work rate increments, it allows patients to have full control over the test, and it ensures that regardless of fitness all patients will be exercise for the recommended test time. The fixed test duration of 10 minutes may also help to improve the efficiency of running busy CPET clinics. There are clear benefits to using the SPV, although further research is required first to assess its ability of predicting postoperative outcome in a much larger sample, and to determine if it can be used to the same advantages sCPET protocols have previously demonstrated.