In 12 normal subjects, use of ear densitography permitted measurement of systolic time intervals (STI) during uninterrrupted treadmill exercise to over 90 percent maximal heart rate on a modified Bruce protocol. Results for control (sitting→standing)→ end-exercise at 18 minutes → 10 minutes' sitting recovery were: heart rate (HR): (77→86)→171→98 beats per minute; pre-ejection period (PEP): (106→111)→49→110 msec; ejection time index (ETI) (351→330)→380→366 msec; PEP/LVET (0.42→0.49)→0.29→0.45. Heart rate increased steadily to 18 minutes. In contrast, the PEP/LVET decrease was almost complete by three minutes and both ETI and PEP responses were bimodal with respective plateaus between three and six minutes and three and nine minutes. All STI and HR curves showed rapid restitution during early recovery. The changes during treadmill exercise were numerically comparable to those during bicycle exercise at a common heart rate. The results indicate that it is technically feasible to measure systolic time intervals with precision during uninterrupted treadmill exercise; responses to treadmill exercise were in the direction expected and quantitatively comparable to bicycle exercise at comparable stress level. These observations provide the technical and physiologic bases for applying this method in clinical treadmill exercise testing.
All Science Journal Classification (ASJC) codes
- Pulmonary and Respiratory Medicine
- Critical Care and Intensive Care Medicine
- Cardiology and Cardiovascular Medicine