1. Design The proposed study is of a experimental study design. The study will be subject to approval by the Ethical committee of Khon Kaen University and subjects will be asked to give their written agreement to participate.
2. Subjects Elderly subjects with isolated systolic hypertension will be recruited from primary care units in the community and outpatient department of Srinakarind hospital in Khon Kaen province. Healthy normotensive subjects living independently with normal physical activity will be recruited from the same community.
Inclusion criteria: Subjects should be over 60 years of age with essential isolated systolic hypertension (stage I-II base on recommendation of JNC-VII) for the hypertension group and normal blood pressure in the healthy group. Good communication, independent physical activity. The healthy subject should be non-smokers, non-obese, free of any signs or symptoms of disease as revealed by medical history Exclusion criteria: Essential hypertension stage III or secondary hypertension, any history of respiratory disease, heart disease, renal disease, blindness, cerebrovascular disease, exercise limited by pain Subjects who have passed the inclusion criteria and exclusion criteria will undertake a dynamic exercise test and a static hand-grip exercise pressor test in the cardiopulmonary research room , Khon Kaen University
3. Outcome measurements The main outcome measures will be changes in blood pressure and heart rate during the two forms of exercise.
Blood pressure: Blood pressure will be measured with a digital bedside monitor (Figure 1). An inflatable cuff placed around the subject's arm one inch above the patient's elbow over the brachial artery. Resting blood pressure will be measured in a sitting position after having rested for 15 minutes Heart rate: Heart rate will be measured at rest and during exercise. ECG electrode will be attached in lead II configuration and connected to the BIOPAC system. The heart rate will be determined from the R-R interval with the data analyzed by the BIOPAC system.
4. Procedures and protocol After an interview where they will be informed about the various tests and asked to provide their informed consent, the subjects will undertake two different exercise tests, the order of which will be in a randomized and balanced design. The subjects will be asked not to smoke, take alcohol or caffeinated drinks within 2 hours before testing.
Cycling exercise: The dynamic exercise will be with the subject sitting on a cycle ergometer (Monark 828 E). Resting heart rate will be measured for 2 minutes before the start of exercise. The exercise level will be limited to 50% of the estimated maximum heart rate reserve. Maximum heart rate will be estimated as 207-0.7\*age (Gellish et al., 2007) and heart rate reserve (HRR) as maximum minus resting heart rate. Subjects will pedal at 50 rpm for 1 min with no load and then 3 minutes against a load of 0.5 Kp (25W) increasing to a load of 1 Kp for the next 3 minutes and to 1.5 Kp, if necessary, for a further 3 minutes until the target heart rate of 50% HRR is reached.
Subjects will be asked about their level of perception of dyspnea using a visual analog scale every 3 minutes at the end of each load.
Static exercise pressor response: The static exercise pressor response will be tested using isometric handgrip of the left hand. The forearm will be supported on an arm rest with elbow flexed. The maximum voluntary contraction force will be measured as the best of three attempts. After 2 minute rest, subjects will perform 2 minute of isometric hand grip contraction at 30% MVC. Circulatory occlusion(50 mmHg supra-systolic pressure) will start at 1.30 min and continued for 2 minute after the end of the isometric handgrip exercise. Following release of the cuff there will be a further 2 minutes recovery. The blood pressure and heart rate will be measured at the end of each minute during rest, isometric handgrip, circulatory occlusion and recovery. Subjects will be instructed to breathe normally during the test and avoid any Valsalva maneuver; breathing frequency will be monitored during the handgrip pressor test using capnography.
5. Data and statistical analysis Data will be expressed as mean ± SD. Changes of data during and post test from baseline. Will be tested by paired t-test. Significance were set at P\<0.05.
