Although I couldn’t find evidence-based literature concerning your specific use of TENS, I will try to give your some clarifications concerning your question:
First, what is TENS: Transcutaneous electrical stimulation (TENS) is the application of electrical current through electrodes placed on the skin. Varying frequencies can be applied, from low (< 10 Hz) to high (> 50 Hz). Depending the intensity used, the patients feels from a strong but comfortable sensation to motor contraction (sensory intensity of TENS vs motor intensity of TENS). The most frequent use of TENS is in pain control, but other approaches have been described in the literature (cognitive improvement, blood pressure control, etc...).
The mechanisms of action of TENS is complex and depends on the localisation of the TENS stimulation. For example, it has been shown that in pain control, TENS activates so called “small diameter fiber”s that lead to an inhibition of pain facilitatory pathways from the central nervous system.
TENS effects are mediated by many neurotransmitters such as serotonin, acetylcholine. Additionally, TENS also activate opioid receptors, explaining its role in pain control and noradrenaline receptors, suggesting its role in blood pressure control.
Does a TENS units work by permanently numbing nerve receptors?
The effect of TENS on nerve fibers is dependent on several factors, principally the pulse amplitude and the pulse duration used. Your question doesn’t provide information on how you applied TENS. Experience from pain control studies have shown that activation of large diameter fibres by high frequency TENS leads to more profound and longer lasting inhibition of central pain transmission. Also, the effect of TENS may decline with time due to a phenomen of habituation. These evidences suggest that TENS modulates (either in short term or long term) the function and activity of fiber receptors.
I couldn’t find an example in the literature concerning your specific use of TENS, but it is possible that repeated TENS might have altered neurotransmission of some fibers.
The glans penis is innvervated by the dorsal nerve of the penis. Depending on your location of the TENS, it may be possible that some of these fibers have been “overstimulated” by TENS, leading to the symptoms you are describing.
TENS increases blood flow
I found a study (See in "Sources) that showed that TENS induces a vasodilatator effect on its stimulation site. Interestingly, a trial has been launched in 2016 with the aim to investigate the effect of TENS on arterial stiffness and blood pressure in indivduals with hypertension. So the currently rather sparse evidence regarding TENS and vasodilatator effect has to be confirmed.
Doxazosin is associated with sexual dysfunction
As you have already suggested, sexual side effects is often reported in patients under antihypertensive drugs. Interestingly, in one study investigating the effect of five antihypertensive drugs (acebutolol, amlodipine maleate, chlorthalidone, doxazosin maleate, or enalapril maleate) on sexual function, doxazosine was associated with the lowest incidence of sexual dysfunction. Nevertheless, it is possible that the symptoms you experience may also be linked to doxazosine.
Overall, it is difficult to categorise the symptoms you are describing. From the above points, a mixed aetiology (both the use of TENS and the side effects of doxazine) cannot be excluded. One approach would be to discuss it with your family doctor. If you take doxazosine as an antihypertensive drug, maybe a switch of antihypertensive drug can help unveiling the role of doxazosine in the symptoms you have described.
- Vilela-Martin JF, Giollo-Junior LT, Chiappa GR, et al. Effects of
transcutaneous electrical nerve stimulation (TENS) on arterial
stiffness and blood pressure in resistant hypertensive individuals:
study protocol for a randomized controlled trial. Trials.
- Yang CC, Bradley WE. Neuroanatomy of the penile portion of the human
dorsal nerve of the penis. British journal of urology. 1998. Volume
82, Number 1: Pages 109-113
- Johnson M. Transcutaneous Electrical Nerve Stimulation: Mechanisms,
Clinical Application and Evidence. Reviews in Pain. 2007;1(1):7-11.