NICER-I Chapter 9

Implications for Clinical Practice

Exercise can improve flow-mediated dilation (FMD) in CAD patients [177], and combined hypertension and DM somewhat limit changes in FMD, but not necessarily fitness, body composition or glycaemic control [153]. Further complicating the interpretation of peak SBP outcomes are results in healthy individuals suggesting that a negative relationship may exist between exercise intensity and FMD [178]. Normotensive males with Met-S have also been shown to demonstrate exercise-induced hypertension (EIH), with the best predictors of EIH occurrence being resting SBP and abdominal obesity [179]. Stratification of peak SBP outcomes within SB1 and SB2 (albeit reversed in the latter) subgroups in the current findings may be a reflection of the effects of Met-S on LV morphology independent of age and gender [180], with LV systolic dysfunction further compounded in hypertensive patients [181]. Met-S may also complicate many homeostatic mechanisms as we have discussed previously, including autonomic function and in particular sympathetic mechanisms [182] potentially affecting CVS function. The present MC classification system requires clarification of the differing effects of various combinations of comorbidities, which is a limitation of the current study. Analysis of larger sample sizes in similar manner would provide greater statistical power for more in-depth analysis.

With the exception of a slight difference in peak HR, normotensive SB2 males and females showed very similar outcomes in peak physiology. Males showed relatively consistent post-program increases in EST durations across SB groups. The current findings suggest we can confidently expect lesser outcomes in peal HR and SBP in patients with higher pre-program resting SBP. Thus despite apparent gender-based differences in physiology, sustaining an MI appears to equalise physiological outcomes between normotensive males and females.
It is also important to note that the stratification of peak SBP outcomes based on MC groups seen here in MI patients is the reverse order of that seen in non-MI patients (see Chapter 5). That is, non-MI SB1 patients showed lower peak SBP outcomes post-program as one moves from MC0 to MC4, while the opposite is true in SB1 patients with MI. In SB2 patients, those with no history of MI showed higher outcomes moving from MC0 to MC4, while this is again reversed in MI patients. To the best knowledge of the present author, this study is the first to demonstrate these contrasting outcomes based on a combination of MI history and MC classification.

The altered trend in outcomes following an MI event may potentially be due to the central limitations imposed by the ischemic damage to the heart’s myocardium as a result of the MI, thereby shifting the focus of adaptations more towards the periphery. Thus in hypotensive SB1 patients, an MI event (centrally) and increased MetS comorbidity (systemically) pre-program may be expected to more significantly limit functional capacity pre-program, which leads to greater outcomes in these patients post-program as the CR training reduces these limitations. While the peak SBP outcomes in MI patients appear generally lower than those in non-MI patients (likely due to the central limits imposed by ischemic myocardial damage), the reversal of the MC-based trends may represent the extent to which comorbidities may have been exerting an impact on patients who eventually experienced an MI event. That is, these outcome differences could perhaps be related to the susceptibility of individuals to physiological abnormalities preceding an MI event, with a difference in this susceptibility between the non-MI (lower) and MI (higher) patients.

Comparing outcomes across genders is not straightforward, as various differences discussed previously and in later sections complicate any direct comparisons. In addition to factors already mentioned, gender differences in postural autonomic function with reduced BRS in both genders with age [183] have been demonstrated. The cardiac output and VO2max relationship is similar in both genders at lower exertion levels, but the actual slope of the linear regression is different with men showing overall higher VO2max increases at higher levels of exertion [184] for the same increase in cardiac output. Female gender though has been shown to be a predictor of better LV function in hypertensive patients with LV hypertrophy [185]. There is evidence to suggest that Met-S may compromise FEV1 and FVC, but not FEV1/FVC ratio [57], leading to the development of restrictive lung disease in susceptible individuals. One potential mechanism for this association is inflammation, directly impacting the gas exchange across the alveolar epithelia and pulmonary capillary wall. Whilst such evidence reveals the potential effects of Met-S on systems directly related to aerobic functional capacity, further evidence suggests that common complications presenting to CR may compound the negative effects of Met-S and CVD.

Thus all of these additional factors may be contributing to some of the observed differential outcomes between genders. Patients were able to tolerate elevated peak HR and SBP, and increased EST time, following the investigated IT intervention. However one may instead aim to increase the workload while reducing the cardiovascular burden during exertion. This would signal better physiological efficiency and may be more desirable in a rehabilitation context. This rationale seeking improved increased physiological efficiencies at rest and during exertion is applied within the NICER intervention (see Chapter 15).