Effects of Beta-blockade on Cardiopulmonary Exercise Testing

Summary

Participation Requirements

Description

Study design We propose an interventional study investigating the effects of acute and chronic beta-blockade on cardiorespiratory performance prior to elective surgery. We aim to recruit 64 abdominal aortic aneurysm (AAA) patients under surveillance who will undergo 2 cardiopulmonary exercise tests ...

Study design We propose an interventional study investigating the effects of acute and chronic beta-blockade on cardiorespiratory performance prior to elective surgery. We aim to recruit 64 abdominal aortic aneurysm (AAA) patients under surveillance who will undergo 2 cardiopulmonary exercise tests to investigate the effect of beta blockade on cardiopulmonary performance. This sample size is calculated by using a 2-tailed sample t-test, with 90% power to detect an estimated increase of 10% in oxygen delivery (VO2) at anaerobic threshold. We also estimated a drop-out rate of about 25% which is built into our power calculation estimates. Interventions Patients on long term beta blockade will be studied to investigate the effect of chronic beta blocker use. They will undergo two CPETs, the first on beta blockers, the second after discontinuing their beta blocker for at least 48 hours. Patients not on beta blockers will be studied to investigate the effect of acute beta blockade. They will undergo two CPETs, the first off medication, the second after commencement of beta blockade (weight adjusted, started 48 hours prior to CPET). Potential subjects will be provided with the patient information sheet in clinic, 1-2 weeks prior to their initial CPET. They will be given at least 1 week to consider the study in which the investigators will follow them up via a telephone call. Informed consent to participate in the study will be obtained at their initial (standard care) CPET. All consenting subjects will perform exercise using electro-magnetically braked equipment during a ramped-incremental protocol in two different occasions. Prior to the tests full lung function tests will be performed by body plethysmography. The exercise tests will be performed with subjects wearing nose clips and breathing through a mouthpiece throughout the test. The initial cycling workload will be zero but will progressively increase at a rate of 10-15 Watts/min. After a resting period of 30 seconds and 2 minutes warm up subjects will stop when they can cycle no further. All gas exchange parameters will be measured and a metabolic cart, heart rate and oxygen saturation will be monitored at pre and post testing. Subjects will also be asked to score their perceived breathlessness and leg fatigue using modified Borg scores every minute during exercise, and inspiratory capacity will be measured every minute during the exercise test. At the end of this test, they will be given a date for the 2nd CPET and a prescription for oral bisoprolol once daily (dose adjusted to patients body weight), to be started 48 hours prior to the test (two doses in total). Patients will be informed of potential side effects of the medications at this visit. This will be weight adjusted with a specific dose as follows: 1.25 mg if patent weighs 50-75 kg, 2.5 mg if 75-100 kg and 3.75 mg if >100 kg. Patients will then attend for the 2nd CPET, following which bisoprolol will be discontinued or continued based on clinical indication. If patients are already chronically on a beta blocker, they will have their first CPET while on medication, and then will be asked to stop the medication for a period of 48 hours before the second CPET. It is standard procedure to take the patient off beta blockers prior to their CPET at Aintree University Hospital. Patients will be informed of potential risks of stopping their beta blocker at their first visit. The beta blocker will be restarted or discontinued based on clinical indication after the second CPET.

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