Physiological changes during prone and treadmill exercise

The mean value for the heart rate at stage III of the prone exercise is between the rates at stages 2 and 3 of the Bruce protocol. The mean systolic blood pressures at each stage closely matches that during treadmill exercise. The diastolic

Dexion Frame

Reservoir

7 if Water Cylinder

Reservoir

Figure 9.3. Ergometer for the performance of prone exercise. The feet are attached to the cylinders via cables.

Modified examination couch

Figure 9.3. Ergometer for the performance of prone exercise. The feet are attached to the cylinders via cables.

blood pressure (DBP) response differs in the two techniques since it falls during treadmill exercise and the higher resting prone diastolic blood pressure rises as the workload is increased during prone exercise.

At rest, the oxygen consumption is equivalent before both types of exercise and is similar to the normal values reported by other investigators. The prone exercise oxygen consumption (stage III) compares favourably with that at stage 1 of the Bruce protocol.

In Fig. 9.6 the rate-pressure products of the two types of exercise are shown.

Figure 9.4. Diastolic blood pressure (DBP) at rest and during prone (Pronex) and upright exercise (Treadmill).

Treadmill

Time (Exercise Stages)

Figure 9.5. Total body oxygen consumption (V02) at rest and during prone and upright exercise.

Treadmill Pronex

25000-

15000-

15000-

5000

Time (Exercise Stages)

Figure 9.6. Rate-pressure product at rest and during prone and upright exercise.

High rate-pressure products occur during prone exercise and indeed during the final stage of the prone exercise protocol the rate-pressure products are over 20000 and close to those found during stages 3 and 4 of the Bruce protocol.

3.2. Physiological changes during isometric exercise

Sustained handgrip or isometric exercise is another method which can be used for studying the effects of myocardial stress on the intracellular PCr concentration. The effects of this type of exercise on the circulation are well documented (Lind et al., 1964; Donald et al., 1967). There is a rapid elevation in systolic and diastolic blood pressure which leads to significantly increased afterload. The effects are shown to be transient and generally reverse within 1 min of recovery.

3.3. Cardiac high energy phosphate metabolism during isotonic and isometric exercise

High-energy phosphate measurements during dynamic exercise are shown in Fig. 9.7 for a subject undergoing prone exercise in a 1.9 T whole-body magnet. The exercise was performed using the 5.0 kg workload which was evaluated during the physiological studies. Thus, at a level of exercise which is close to that at stage 1-2 of the Bruce protocol, when the oxygen consumption is 9.2±2.0 vs 14.5±2.9 ml/kg/min (Bruce stage 1) and the rate-pressure product

M.A. CONWAY et al. REST EXERCISE

HEART

CHEST WALL.

-JVM

HEART

-JVM

2 cm

DEPTH.

DEPTH.

2 cm

1 cm ppm

Figure 9.7. Human cardiac spectra acquired during dynamic prone exercise using 3IP MRS (abbreviations as in Fig. 9.1). Reproduced with permission from Conway et al. (1991b) BMJ Publications.

is 12670±3580 vs 12290±3028, no change develops in the PCr/ATP ratio (rest, 1.56±0.2; exercise, 1.58±0.14).

Similar observations have been made by Weiss etal.(1990) using an isometric exercise for 7-8 min at 30% of maximal voluntary contraction. Two minutes were allowed to achieve steady state before signal acquisition. Spectra from normal controls which do not alter during isometric exercise have also been acquired by Yabe etal.{ 1994).

These findings demonstrate that during both isotonic and isometric exercise the PCr/ATP is unchanged in normal subjects. Thus, despite an increase in workload associated with measurable significant haemodynamic changes, the cellular PCr content is unaltered.

Several questions about normal cardiac metabolism still remain to be answered, e.g. can MRS be used to demonstrate the absence of change in the PCr level with each contraction in the normal heart, as has been shown by

Table 9.2. Examples of direct measurements of high-energy phosphates in models of ventricular hypertrophy and heart failure.

Preparation and

Publication

experimental detail

Cr"

PCr"

ATP"

Hochrein and

GP, in situ

N

7.2

3.5

Döring (1958)

Vol. load+ +

CHF

-32%

-11%)

Feinstein

GP, in situ

N

8.4

5.6

(1960)

(Aortic constriction)

CHF

-54%

-24%

Pool et al.

Cats, RVH

(1967)

Right ventricle:

N

15.5±0.6

7.2±0.5

5.1 ±0.2

RVH

12.5±0.9

5.4±0.5

5.1±0.4

CHF

9.70+0.6

4.1 ±0.4

5.1+0.6

Left ventricle:

N

17.4±0.5

7.9±0.7

5.8±0.3

LVH

17.0±1.3

8.8±1.0

6.3+0.6

CHF

12.2±0.4

5.9±0.8

6.0±0.6

Coleman et al.

Dogs, Sham op. («=8)

21.3±0.8

9.0±0.6

6.4±0.3

(1971)

Ch Tachy CHF («=6)

13.8±0.6

7.1±0.6

5.4±0.7

Attarian et al.

Dogs, Subendo

Con

42.1+0.9

23.8±0.7

(1981)

LVH

27.1 ±3.6

18.2±1.7

Dogs, Subepi

Con LVH

45.6±1.9 41.2±2.5

23.5±1.0 22.4±0.7

Creatine (Cr); phosphocreatine (PCr) adenosinetriphosphate (ATP); congestive heart failure (CHF); left-ventricular hypertrophy (LVH); guinea pig (GP); control (CON); normal (N); tachycardia (Tachy); subendocardial (Subendo); subepicardial (Subepi).

Creatine (Cr); phosphocreatine (PCr) adenosinetriphosphate (ATP); congestive heart failure (CHF); left-ventricular hypertrophy (LVH); guinea pig (GP); control (CON); normal (N); tachycardia (Tachy); subendocardial (Subendo); subepicardial (Subepi).

Wikman-Coffelt et al. (1983)? Can 31P MRS reliably demonstrate different metabolic concentrations in the epicardial compared with the endocardial segments? Such questions represent significant technical challenges at present but are an important part of future strategy since PCr/ATP ratios measured during diastole or systole alone or as a mean measurement across the myocardium may fail to differentiate clearly the demands on PCr metabolism - both in controls and in patients with ischaemia and other cardiac disease.

Run for Your Life The Health Benefits Of Treadmills

Run for Your Life The Health Benefits Of Treadmills

Improve your hearts health? Lose a few pounds? Or simply become more active? If that is your goal, then maybe its time for you to do some exercise. But where do you start?

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