Acute Physiological Responses to Different Exercise Modalities in Patients with Chronic Heart Failure P. FERENTINOS1,2, L. KARATZANOS2, S. DIMOPOULOS2, G. MITSIOU2, E. ZERVA2, E. KALDARA3, C. TSAKIRIDES1, S. NANAS2 1 Carnegie Faculty of Sport and Education, Leeds Beckett University, Leeds, UK. 2 Cardiopulmonary Exercise Testing & Rehabilitation Laboratory, School of Medicine, N & K, UOA, Greece. 3 3rd Cardiology Department, School of Medicine, National & Kapodistrian University of Athens, Greece. Introduction Aerobic exercise is a key component in rehabilitation programmes for patients with chronic heart failure (CHF). Besides continuous training, in recent years, there has been an increased interest for high intensity interval training which seems to be more efficacious and better-tolerated. The purpose of the study was to compare the acute cardiopulmonary responses between a high intensity aerobic interval training protocol (AIT) and a continuous training protocol (CT) in patients with stable CHF. Results There were no differences in mean haemodynamic responses (O2 pulse, heart rate) (P > 0.05, table 3). No significant differences observed in mean ventilation (VE) and in mean carbon dioxide production (V̇CO2) (table 3). Total oxygen consumption in AIT was higher (P < 0.01) while the mean % V̇O2peak was higher during CT (P < 0.05) (table 3). Patients exercised significantly longer at > 90% V̇O2peak (P <0.05) during the AIT session (Figure 1) with no difference in RPE (P > 0.05). Completion rate in both protocols was 100% without any abnormal blood pressure response or any significant ventricular dysrhythmias. Methodology Fourteen stable CHF male patients at optimal medical treatment (Table 1) volunteered for the study. Patients performed a symptom limited cardiopulmonary exercise test for the prescription of the AIT and CT protocols. On separate days and in a random order the patients performed one AIT and on CT session (Table 2). Table 3. Cardiopulmonary responses during AIT and CT.   AIT CT P VE (L.min-1) 40.3 + 8.1 40.7 + 8.4 0.52 O2 pulse (mL.beat) 12.9 + 3.2 13.1 + 2.7 0.30 HR(beats.min-1) 91 + 11 93 + 12 0,17 O2 consumption (L) 36.8 + 10.8 34.4 + 9.9 < 0.01* V̇O2 (%peak) 77.5 + 6.0 80.9 + 6.0 < 0.05** V̇CO2 (mL.min-1) 1122 + 343 1147 + 365 0,13 RPE (Borg scale) 13.3 + 2.5 11.6 + 3.0 > 0.05 Results are reported as mean + SD. *P < 0.05, **P < 0.01 Table 1. Patients clinical characteristics.  (n =14, LVEF < 45%) Age (years) 55 + 14 V̇O2peak (mL· kg-1· min-1) 18.7 + 4.4 VAT% V̇O2peak 62.0 + 6.7 Body mass index (kg/m2) 27.0 + 4.4 NYHA classification (Ι / ΙΙ /ΙΙΙ) 3 / 9 / 2 Weber class (A / B / C) 5 /6 / 3 Etiology of heart failure(dil* / isch*/ other) 4 / 8 / 2 Results are reported as mean + SD on n (%). VAT, ventilatory anaerobic threshold *dil – dilated cardiomyopathy, * isch – ischaemic heart disease. Table 2. Characteristics of the AIT and CT protocol. Protocol Exercise - Intensity Rest - Intensity AIT (4 sets) 4 min at 80% V̇O2peak 3min at 50% V̇O2peak CT 70% V̇O2peak - * The duration of the CT protocol adjusted so that the total work performed matches that of the AIT session. The duration during the CT varied in every patient. Figure 1. Time spent > 70%, > 80%, > 90% of V̇O2peak. *significant different, P < 0.05. Summary and Conclusion Both protocols elicited a strong physiological stimulus with the same haemodynamic responses and same ventilatory demand. The AIT protocol allowed patients to exercise for a longer time at > 90% V̇O2peak which may explain the physiological adaptations derived from the application of this type of training. Both protocols were safe and well-tolerated by the patients. Acknowledgements This work is supported by the Carnegie Research Fund.