These contents would introduce (a) the clinical linking between ED and CVD and vice versa, along with the risk factors of CVD in ED patients, and (b) the CVD risk stratification for the severity of heart failure and stroke in ED patients based on AI. One can use the risk factors such as office-based biomarkers (OBBM), laboratory-based biomarkers (LBBM), carotid ultrasound image phenotypes (CUSIP), and medicine usage (MedUSE) combined with ED covariates for designing knowledge-based systems for CVD prediction. Thus, ML and DL solutions can help in establishing the early CVD risk assessment of ED patients who are at a high risk of CVD or ischemic and hemorrhage stroke.
2. Erectile Dysfunction and Cardiovascular Disease Links: Clinical Evidence
The definition of a health risk is “a characteristic or incident that is associated with a higher probability of a certain result, such as the occurrence of a disease.”
[54]. The Framingham Heart Study is a major milestone in terms of identifying risk factors for CVD. The FHS’s work has considerably helped preventive medicine. As a result, the focus shifted from treatment to prevention and education
[55]. All combined atherosclerotic plaque risk factors should be considered relevant to CVD
[56]. Age, gender, a family background of CVD, and ethnicity should be considered as non-modifiable CVD risk factors. Age is an indicator of duration, and it is linked to CVD risk. Age is also the largest indicator affecting cardiovascular outcomes
[57][58]. Another well-known CVD risk factor is the male gender. According to the FHS data, women’s CVD mortality is equivalent to that of males 10 years younger
[59]. Another well-established, non-modifiable risk factor is a first-degree relative with a history of CVD
[60][61]. This link is especially robust in younger people who have a strong family history of premature illness
[62][63]. Even though these risk variables are non-modifiable, their identification is important in clinical treatment because it helps in identifying individuals who require more stringent control of modifiable CVD risk factors.
In addition to ischemic heart disease, stroke, and peripheral artery disease, hypertension has been linked to several of the most significant atherosclerotic symptoms, including peripheral artery disease (PAD)
[64][65]. In the normal BP range (>115/75 mmHg), there is no solid evidence of a risk threshold for CVD
[65]. This link has been seen in people of all ages, and it appears to be greater for systolic BP than diastolic BP
[66][67]. Stroke and heart disease fatalities increase more than multiple times for those aged 40–69 years who have an increase in their blood pressure of 20 or 10 mm Hg
[65].
Diabetes mellitus (DM) doubles or triples the risk of myocardial infarction or stroke, as well as the risk of CVD mortality
[68][69]. This risk rises in proportion to the degree of glycemic change
[70]. Intermediate carbohydrate metabolic anomalies have also been linked to a higher CVD risk
[71][72]. In contrast to diabetes, diabetic people have a higher risk of CVD due to the existence of additional metabolic abnormalities
[73].
ED is generally referred to as a vascular disease, and it is generally known that it shares several health risks with CVD, including obesity
[32][74], chronic renal disease
[75], poor socioeconomic status
[58], low fruit and vegetable consumption
[76], inadequate physical activity
[77], metabolic syndrome
[78][79], and elevated C-reactive protein levels
[80], which are all well-known risk factors for CVD. In this context, a large prospective study evaluating the effect of CVD risk variables on ED over 25 years showed that age, BMI, cholesterol, and triglycerides were all highly associated with ED
[79]. Smoking, BMI, hypertension, cholesterol dietary consumption, and unsaturated fat intake have all been linked to an increased risk of ED
[78][81].
Figure 2 indicates the shared risk factors of ED.
Figure 2. Shared risk factors of ED.
Therefore, in connection, ED affects around 75% of diabetes patients over the age of 60 and grows proportionately with the severity of the condition
[82]. It is possible that ED and penile atherosclerosis are the common denominators between ED and diabetes
[83]. However, the link between these two clinical diseases is complex, and additional pathophysiologic processes, such as autonomic neuropathy and hormonal abnormalities, may be involved in the development of these two clinical conditions
[22][84].
2.1. The Pathophysiologic Link between ED and CVD
The pathophysiology of ED is dependent on the integrity of the endothelium
[85][86]. Sexual drive induces the production of NO and other endothelial mediators, resulting in stimulating sympathetic stimulation in the veins feeding penile regions and an enhanced blood flow to the penis while blocking the vein discharge
[86][87]. These occurrences cause blood to be trapped within the corpora cavernosa. This increase leads to system pressure and an erection
[88]. The carotid arteries hypothesized that ED and COAD have the same involvement in the pathogenesis pathway
[89]. ED and circulation stenosis may result from exposure to known risk factors. Due to the systematic character of atherosclerosis, all arterial pathways may be harmed to the same amount, but the onset of signs is linked to arterial size
[9][90]. Increased vascular tolerance for the same amount of endothelial dysfunction and/or atherosclerotic burden is observed in bigger vessels when compared to smaller arteries
[91]. Alongside the more compact ones, penile veins are smaller than other veins in the body
[92]. Compared to coronary arteries, they are tiny, (1–2 mm) to (3–4 mm), with endothelial dysfunction at the very same level, and atherosclerosis may cause a greater decline in blood flow
[9].
Consequently, the vascular system of the penile organ may serve as an early warning system for a wide range of vascular conditions
[93]. Individuals with chronic coronary syndromes (CCS) are more likely to have ED than those without CCS, according to this hypothesis. In this respect, Montorsi et al.
[3] explained that for patients with chronic coronary syndrome, ED is common before CAD symptoms appear. Most patients with CCS begin to have sexual dysfunction three years before any cardiac symptoms appear. This contrasts with the rarity of sexual dysfunction in those suffering from acute coronary syndrome
[3]. Appropriate arterial penile lesions were found in only 12.9% of the cases, compared to a high frequency of 87% in the coronary system and 77% in the internal iliac artery area
[94].
Figure 3 shows the CVD risk factors linked with inflammation, androgen, and endothelial dysfunction.
Figure 3. CVD risk factors are linked with inflammation, androgen, and endothelial dysfunction.
A comprehensive reformulation of all available evidence revealed that, while the artery-size theory is crucial to understanding the complicated relationship between ED and COAD, vasculogenic ED is also connected with dynamic, macroscopically intangible irregularities linked to endothelial dysfunction and neurogenic hyperactivity
[42]. The usual indications of cardiovascular problems are quite often disguised in diabetics, causing a diagnostic lag of COAD and difficulty in altering the disease’s natural history
[95]. In diabetes patients, an individual relationship between ED and asymptomatic COAD has indeed been described
[96][97]. Endothelial functioning is affected by low-grade inflammatory cytokines, which can lead to a thrombogenic state
[98]. Several studies have linked the development and intensity of ED to the elevated expression of inflammation biomarkers
[44][45][46][47]. The major targets for androgen actions inside the penile and cardiovascular pathways are endothelium and sleek cells, and congenital hypothyroidism is associated with an increased risk of arteriosclerotic remodeling
[99][100].
As a result, it is found that people who have ED and risk factors for cardiovascular disease are more likely to have a “silent COAD.” They should get a full CVD examination.
Mechanism of Penile Erection
The mechanism of the male penile erection, as well as cross-section, is shown in
Figure 4A,B, where the aorta is directly connected to the penal artery. A significant blood input is essential for successful sexual performance
[101][102]. As previously stated, normal penile erection is a neurovascular event that causes sexual stimulation and the release of NO hormones from endothelial cells
[103][104].
Figure 4. (A) Mechanics of penile erection (courtesy of AtheropointTM, Roseville, CA, USA). (B) Cross-sectional of the penis (courtesy of AtheropointTM, Roseville, CA, USA).
As a result, strong blood flow from the heart to the penal muscle cells is required for a proper erection
[105][106]. All these processes cause blood to be caught inside the corpora cavernosa (
Figure 4B), resulting in intracavernous pressure and an erection
[107].
2.2. The Effect of SARS-CoV-19 on Erectile Dysfunction
SARS-CoV-2, the interaction of the enhanced ACE2 and the transmembrane protease serine 2 with a component of the spike protein, accelerates binding and transit into vascular endothelium cells
[108]. According to the studies, endothelial dysfunction is a significant contributor to COVID-19 symptoms
[109][110]. The
Table 1 show the relationship between ED with CVD or coronary artery disease. Direct viral invasion of testicular tissue via ACE2 receptors, temperature-related testicular injury resulting from sustained high fever, inflammatory and autoimmune responses, and viral infection-related oxidative stress are some of the suggested causes of this damage
[111][112].
Figure 5 explains the biological link between ED and CVD/Stroke and
Figure 6 validates the biological link between SARS-CoV-19 with ED.
Figure 5. The biological link between ED and CVD/Stroke. RoS: reactive oxides stress, NO: nitric oxide, Up Arrow: depicts increase, Down Arrow: depicts decrease.
Figure 6. The biological link between COVID-19 and ED. RoS: reactive oxides stress, NO: nitric oxide, Up Arrow: depicts increase, Down Arrow: depicts decrease.
Table 1. The studies show the relationship between ED with CVD or coronary artery disease.
Endothelial cells infected with SARS-CoV-2 suffer endothelial damage, which causes thromboembolic vascular lumen alteration in the endothelium, immune thrombosis, and reversal in many organs
[123]. These are the ultimate and noticeable consequences of the cells taken by SARS-CoV-2 from the endothelium
[124]. ED is one of the most common symptoms of COVID-19, which is caused by endothelial dysfunction
[123]. This can result in circulatory problems in numerous organs
[109][110]. This includes a reduction in blood supply to the testicles, which can lead to ED. Natural nitric oxide (NO), generated by healthy endothelial cells, is an essential cofactor in the endothelium-dependent phase transition in the corpora cavernosa
[125]. Endothelial dysfunction is caused by a decrease in eNOS expression, which results in a decrease in NO production
[126][127]. Increased endothelium-bound cavernosal tissue vasodilation is associated with hypertension and diabetes
[128].
People were experiencing psychological trauma, as well as the overall feeling of a high degree of uncertainty associated with the COVID-19 global epidemic
[129]. The restrictive measures that were implemented during this critical period, in the long term, influenced interpersonal and intimate relationships
[130]. Concerns about safe intimate/sexual interplay, the forced separation of intimate partners, the escalation of marital disputes, and degradation in contact are some of the most significant contributors to a person’s experience of sexual troubles and sexual unhappiness at this age
[130][131][132].
Sexual desire and expression differences, as well as a lack of privacy while confined, have both been linked to the development of sexual difficulties and dissatisfaction
[133][134]. COVID-19 infection, on the other hand, has the potential to negatively impact male sexual function by inducing endothelial damage, which can result in erectile dysfunction, testicular injury, and psychological alterations
[134][135].
It can be hypothesized that erectile dysfunction occurs more frequently in the presence of heart issues when the endothelium and smooth muscle are dysfunctional. Endothelial dysfunction impairs blood flow to the heart and the penis, contributing to the development of atherosclerosis.