Proportional Internal Work—a New Parameter of Exercise Testing in Study of Health in Pomerania (SHIP)

Abstract

Purpose: Cardiopulmonary exercise testing usually requires a maximal exhaustive effort by the patient and is time consuming. The purpose of this study was to assess whether the cost to initiate exercise termed “proportional internal work” (PIW) was related to cardiovascular disease (CVD) risk factors, ventilatory parameters, and mortality. Methods: We used data from population-based Study of Health in Pomerania. A total of 2829 (49.5% female) study participants with a median age of 52 (42-62) yr were included. Standardized questionnaires were used to assess CV risk factors. The cardiopulmonary exercise testing was performed using a modified Jones protocol. Regression models adjusted for sex and age were used to relate PIW with CVD risk factors and ventilatory parameters. The PIW was calculated by the following formula: (Oxygen uptake at rest – Oxygen uptake without load)/V˙o 2peak) × 100. Cox regression analysis was used to relate PIW and all-cause mortality. Results: We identified a nonlinear association between PIW and percent predicted V˙o 2peak. Women had a 2.96 (95% CI, 2.61-3.32) greater PIW than men. With each year of age and every point in body mass index, the PWI increased by 0.04 (95% CI, 0.03-0.05) and 0.16 (95% CI, 0.12-0.20), respectively. After adjustment for age, sex, smoking, and body mass index, a 1-point greater PIW was associated with a 5% higher risk to die (HR = 1.05; 95% CI, 1.01-1.07). Conclusions: The PIW is a new cardiopulmonary exercise testing parameter related to CVD risk and all-cause mortality. Future studies should assess the prognostic relevance of PIW for CVD prevention.

Metabolic cost of unloading pedalling in different groups of patients with pulmonary hypertension and volunteers

“…In our study we showed that patients have a similar PIW compared to healthy individuals from the general population. In 580 patients as well as in 354 SHIP controls the PIW was between 14 and 15%, which correspondents well with the PIW of 14.7%, which we previously reported for the whole SHIP-cohort 14 . While the PIW did only differ slightly between the patients and the SHIP controls, the PIW (Watt) was significantly higher in the patients than in the SHIP controls (18.0% vs. 15.9%).…”

“…This indicates that the PIW may be a useful screening parameter in healthy individuals independent of the CPET protocol. In a previous analysis based on SHIP data, we demonstrated that a higher PIW was associated with a higher risk to die 14 . Future studies are needed to reveal, whether the PIW adds predictive value independent of established cardiovascular risk factors such as age, sex, BMI, blood pressure, diabetes or dyslipidaemia.…”

“…1 ). Furthermore, we calculated the simple IW (ml/min) as difference of VO 2 @unload and VO 2 @rest 14 .…”

“…According to Shah et al we calculated the PIW (IW(Watt)/Watt max in %) as the ratio of IW (Watt) to the total work (in Watt) 13 . Additionally, we calculated the simple PIW by the following formula: ((VO 2 @unloading − VO 2 @rest)/VO 2 @peak)*100 14 .…”

“…In the Framingham Heart Study (FHS), IW was positively associated with cardiovascular risk factors in healthy subjects as well as in heart failure patients with preserved Ejection Fraction (HFpEF) 13 . In a recent analysis from our group a higher proportional IW (PIW = IW divided through peak oxygen uptake [VO 2 ]) was associated with a higher all-cause mortality in healthy individuals of the population-based Study of Health Pomerania 14 . However, it is so far unclear whether IW and PIW are good markers to differentiate other patient groups than HFpEF from healthy individuals.…”