Question About Dr. Peat's Assertions On Stair Step Heart

[ecstatichamster]

I understand Dr. Peat to say that the faster heart rate, from say fixing hypothyroid, increases the stroke volume as well as the heart rate.

But this would mean that a higher heart rate increases the blood flow sort of 2 X. More beats, and more volume of blood per beat.

I was telling a medical friend this and she said:


Cardiac output (CO)= stroke volume (SV) X heart rate (RR). Homeostasis determines cardiac output in each individual and it stays relatively constant when not exerting oneself. The two are inversely proportional in order to keep cardiac output relatively constant in resting patients. I did not infer the same thing that you did from this article. When NOT exercising, in the cardiac normal human, volume of heart stroke (SV) does NOT increase along with heart rate. This would raise cardiac output to above homeostatic levels. This only occurs in exercising patients, in which the demand for oxygen causes the cardiac output to increase. otherwise then two values adjust up or down inversely in order to maintain a relatively constant cardiac output during rest. Volume of heart stroke decreases as heart rate increases, in order to keep CO relatively constant in the resting state. This physiological fact, I was taught, in undergrad as well as vet school cardiac physiology lectures.
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So what's right? I am sure Dr. Peat is right, but I don't fully understand.

 

[Blossom]

I think your friend is partially correct but she is speaking of ‘cardiac normal’ and Peat is speaking about hypothyroidism.
If the heart is pumping slow and weak (or just slow or just weakly) from poor thyroid function or metabolism then blood flow isn’t going to be optimal. My take on Peat is that thyroid hormone will increase both the heart rate and strength of the muscle contraction by providing adequate energy. I could be wrong in my understanding of course.
I don’t think most medical people appreciate the actions of thyroid hormones the way Peat does. That’s not meant in a dismissive way at all-it’s simply not part of the curriculum as far as I’m aware.

 

[aguilaroja]

I understand Dr. Peat to say that the faster heart rate, from say fixing hypothyroid, increases the stroke volume as well as the heart rate.
But this would mean that a higher heart rate increases the blood flow sort of 2 X. More beats, and more volume of blood per beat.
I was telling a medical friend this and she said:
Cardiac output (CO)= stroke volume (SV) X heart rate (RR). Homeostasis determines cardiac output in each individual and it stays relatively constant when not exerting oneself. The two are inversely proportional in order to keep cardiac output relatively constant in resting patients.... When NOT exercising, in the cardiac normal human, volume of heart stroke (SV) does NOT increase along with heart rate ...

...thyroid hormone will increase both the heart rate and strength of the muscle contraction by providing adequate energy. ..
I don’t think most medical people appreciate the actions of thyroid hormones the way Peat does....

Thyroid hormone can influence both
heart rate (chronotropism) AND
stroke volume, through heart muscle contractility (isotropism)

Thyroid hormone can also change heart excitability (bathmotropism) and heart muscle filling/relaxation (lusitropism).
Added to all this is thyroid effects on peripheral circulation and metabolic fluid exchange.

There are stereotypical physician ideas of hyperthyroid and hypothyroid effects generally. In discussions of thyroid effects on the heart, things may be equally muddled. The heart performance in youthful states, which tend to coincide with better thyroid function, is a clue to improved understanding.

 

[marsaday]

My hr does not increase with thyroid hormone. It’s a bit of a mystery why I have such a low hr.

Always at resting in teens was 48 beats/ min

Now in 40’s and on t4 it’s in the lower 40’s.

I am older but I am healthier now than when in my 20’s and hypothyroid.

Temps are good and I generally feel well but hr never comes up. I can get up to 180 with intense exercise still

 

[yerrag]

I think the doctor is thinking in terms of the body's circulation operating on a constant flow rate. So he thinks that if heart rate increases, the stroke volume has to decrease. That makes sense from an efficiency standpoint. The less strokes needed, the more efficient the heart. This is consistent with the conventional medical thought that a low heart rate is a sign of health.

Not that he is always always wrong to think that way. There are instances when that conclusion is correct. Such as when blood carries less than the maximal amount of oxygen (in emphysema, mercury toxicity), but this isn't about constant flow, but about more flow needed, and a higher heart rate needed to deliver an equal amount of oxygen.

Or when the blood has a sub-optimal amount of CO2 to effect the release of oxygen to tissues optimally. A higher heart rate would be needed to effect a higher flow rate to effect a requisite amount of tissue oxygenation.

But even with no hypoxemia and with enough serum CO2, it's still flawed to model the heart as a motor that delivers blood at a fixed flow rate.

The demand for oxygen by tissues also determines the flow rate. And the demand for oxygen is dependent on how efficiently the oxygen (and sugar) is used to produce energy, and how much energy is being used by the body to keep itself functioning, be it in survival mode, or in an optimal health mode, or anywhere in between.

As thyroid pushes the body towards being more efficient in producing energy, and its effect on contributing to better health, it will create an energy demand that determines its capacity to take in oxygen, and this set the flow rate of blood needed. This will affect the heart rate. The heart rate is demand driven, and with the demands needed to maintain a healthy and fully functional system, it will need to be high, even with the heart being efficient.

The demand for oxygen is greatest at peak health, where energy is in surplus that it can be used for development - skin, hair, virility, intelligence, intuition etc. This is reflected in a strong heart rate. But a strong heart rate can also be a sign of poor health, because of the inefficiency brought upon by poor health.

I guess the doctor has only seen cases of poor health, and her universe defines her view on heart rate.

 

[aguilaroja]

Hypothyroidism and the Heart
"Hypothyroidism can result in decreased cardiac output, increased systemic vascular resistance, decreased arterial compliance, and atherosclerosis.

Impaired cardiac muscle relaxation, decreased heart rate, and decreased stroke volume contribute to heart failure in hypothyroidism.

Subclinical hypothyroidism is associated with ischemic heart disease and increased cardiovascular mortality.

 

[GreenEyedBlonde]

My hr does not increase with thyroid hormone. It’s a bit of a mystery why I have such a low hr.

Always at resting in teens was 48 beats/ min

Now in 40’s and on t4 it’s in the lower 40’s.

I am older but I am healthier now than when in my 20’s and hypothyroid.

Temps are good and I generally feel well but hr never comes up. I can get up to 180 with intense exercise still

This is same for me. HR in high 40’s to low 50’s for many years. I’ve been taking T4 for Hashimoto’s and my latest TSH was 0.06 and my T4 was mid range. Can get my HR up with exercise but temps always around 96 degrees F. Endo says to decrease T4 based on TSH. Go figure - HR will probably end up in low 40’s.