I noticed my HRV (heart rate variability), seems to drop a lot when I take GH before bed any idea why this would happen ?
Whenever we're talking HRV, on a board like this, we must unpack:
For starters, let's dismiss with all illusions: HRV is primarily a measure of cardiac function. We refer to the autonomic nervous system, the Russians and those researchers and practitioners within their spheres of influence refer to this as the vegetative system and speak of variable phase and somatic states.
At bottom, heart rate variability (HRV) is defined as the variability in the interbeat (R-R) interval (or the N-N interval after abnormal beats have been eliminated from a recording), and is a measure of the state of arousal of the autonomic nervous system such that higher HRV reflects higher parasympathetic activity or tone, reflecting a state of transition to regeneration of homeostasis of the organism [
comrade], etc.
rMSSD is defined as the square root of the mean squared successive differences of interbeat R-R interval.
SDNN is defined as the standard deviation of the N-N interval (after abnormal beats have been eliminated from a recording).
Short time samples can be evaluated in the time domain, i.e., analyzed for the variability in the difference in successive beats (ms).
Longer HR recordings can be analyzed in the frequency domain - sometimes referred to as a power spectral analysis - where HRV fluctuates with varying frequencies.
The
time domain measures of HRV are analogous to measuring the overall flux of light from a star.
The
frequency domain measures of HRV are analogous to analyzing the spectrum of frequencies of light emanating from the star to provide insight into its chemical reactions and composition (120).
Note: Thanks are owed to Dr. Scott Stevenson for his most vivid descriptions of these HRV aspects.
Finally, after these definitions, we can establish that, using acromegaly as a model of GH/IGF-I excess, HRV is suppressed in these patients because of effects on cardiovascular function and by virtue of those effects, on sympathetic tone. [1].
Note: I have discussed the
practical limitations that might fairly be summarized as uselessness of using HRV to estimate changes to strength, i.e., performance for resistance training sessions in the weight room here:
View: https://www.youtube.com/watch?v=VU4LA2-n_1Q
This is because changes in muscular strength or performance are primarily mediated by changes in excitation-contraction coupling and calcium ion fatigue rather than cardiac function.
From [1]:
Results: Acromegalic patients showed significantly lower SDNN and SDANN compared to controls. Diabetic and non-diabetic acromegalic patients showed decreased SDNN and SDANN, when compared to healthy subjects. Diabetic acromegalic patients had a lower LF/HF ratio during 24 h when compared to non-diabetic acromegalic patients. Similar results were obtained analyzing patients affected by acromegaly and impaired glucose tolerance. SDNN and SDANN were lowered by hypertension in the acromegalic population, when compared to controls, and hypertensive acromegalic patients also displayed a decreased LF/HF ratio during 24 h when compared to normotensive acromegalic subjects. Patients with ventricular arrhythmias in Lown classes 3-5 showed a decreased SDANN compared to patients in Lown class 0-2. The treatment with SSAs was able to ameliorate all the time domain parameters of HRV, without altering the 24 h LF/HF ratio.
Conclusion: Cardiac autonomic functions and sympathovagal balance are altered in patients affected by acromegaly and could be ameliorated by SSAs [somatostatin analogues, that block GH hypersecretion] therapy. HRV analysis allows an estimation of the autonomic sympathovagal balance and may be a useful clinical tool for the cardiac risk stratification in acromegalic patients.
[1] Comunello A, Dassie F, Martini C, De Carlo E, Mioni R, Battocchio M, Paoletta A, Fallo F, Vettor R, Maffei P. Heart rate variability is reduced in acromegaly patients and improved by treatment with somatostatin analogues. Pituitary. 2015 Aug;18(4):525-34. doi: 10.1007/s11102-014-0605-6. PMID: 25261332.