Friction in Myocardial Anoxia Leads to Negative Excess Entropy Production, Self-Organization, and Dissipative Structures.

Contraction of the heart is caused by actin filaments sliding along myosin filaments. This generates a frictional force inducing wear of the contractile apparatus. We postulated that this process could be exacerbated when the heart was submitted to severe anoxia. Anoxia induced dramatic abnormalities in the molecular properties of actin-myosin crossbridges. We applied the formalism of far-from-equilibrium thermodynamics to the left ventricular papillary muscles (LVPMs) of mammalian rat hearts which had been subjected to a prolonged anoxia (3 h). We showed that when subjected to prolonged anoxia, the heart operated far-from-equilibrium as evidenced by the non-linearity between thermodynamic force (F/T: Frictional force/Kelvin temperature) and thermodynamic flow (v0: myofilament sliding velocity). The rate of entropy production (EPR) was the product of (F/T) and v0. The excess entropy production (EEP) was equal to ∂δ2S∂t = ∂FTδvo; (S: entropy). The tribological system remained stable when EEP was positive and became unstable when EEP became negative, thus characterizing instability of the system and reflecting the occurrence of self-organization and possibly dissipative structures. After 3 h anoxia, re-oxygenation induced significant reversibility. About 20% of the myosin heads did not recover despite re-oxygenation. These results may be of importance in the context of heart transplantation where the delay between the time of sampling from the donor and the time of the graft installation in the recipient should be as short as possible.

Opportunistic screening for hypertension in the general population in Greece: International Society of Hypertension May Measurement Month 2019.

Hypertension remains a major public health issue with inadequate control worldwide. The May Measurement Month (MMM) initiative by the International Society of Hypertension was implemented in Greece in 2019 aiming to raise hypertension awareness and control. Adult volunteers (≥18 years) were recruited through opportunistic screening in five urban areas. Information on medical history and triplicate sitting blood pressure (BP) measurements were obtained using validated automated upper-arm devices. Hypertension was defined as systolic BP ≥140 mmHg and/or diastolic ≥90 mmHg, and/or self-reported use of drugs for hypertension. A total of 5727 were analysed [mean age 52.7 (SD 16.6) years, men 46.5%, 88.3% had BP measurement in the last 18 months]. The prevalence of hypertension was (41.6%) and was higher in men and in older individuals. Among individuals with hypertension, 78.7% were diagnosed, 73.1% treated, and 48.3% controlled. Awareness, treatment, and control of hypertension were higher in women and in older individuals. Hypertensives had a higher body mass index (BMI) and were more likely to have diabetes, myocardial infarction and stroke, and less likely to smoke than normotensives (all P < 0.001). Among treated hypertensives, 65.1% were on monotherapy, and with increasing number of antihypertensive drugs the BP levels were higher and hypertension control rates lower. The prevalence of hypertension in Greece is high, with considerable potential for improving awareness, treatment, and control. Screening programmes, such as MMM, need to be widely implemented at the population level, together with training programmes for healthcare professionals aiming to optimise management and control.

Thermodynamic bifurcation in anoxic heart: A far-from-equilibrium dissipative structure.

Thermodynamic consequences of a three-hour long anoxia were investigated on the isolated mammalian rat myocardium. The anoxic heart operated in a far-from-equilibrium manner as attested by the non-linearity between the thermodynamic force and the thermodynamic flow. When subjected to slight fluctuations due to anoxia, the open far-from-equilibrium cardiac system presented a thermodynamic bifurcation at ~ 60 minutes of anoxia. The bifurcation was characterized by a sudden change of direction in the bifurcation diagram of a one-dimensional nonlinear differential equation with one parameter and occurred at a non-hyperbolic fixed point at which moment the heart lost its thermodynamic stability. The parameter of the differential equation was the single force of the myosin molecular motor. These results helped to reflect a self-organized process and the occurrence of a dissipative structure. This offers valuable insights into our understanding of myocardial protection and could be of considerable interest, especially for heart transplants where the recipient must benefit from the donor's heart in the shortest possible time.

Prevalence, awareness, and control of hypertension in Greece before and after the COVID-19 pandemic: May Measurement Month survey 2019-2022.

OBJECTIVE: The COVID-19 pandemic had an adverse impact on several cardiovascular risk factors. This study investigated the prevalence, awareness and treatment of hypertension in Greece before and after the pandemic. Data were collected in the context of the May Measurement Month (MMM) global survey initiated by the International Society of Hypertension. METHODS: Adult volunteers (age ≥ 18 years) were recruited through opportunistic screening in public areas across cities in Greece in 2019 and 2022. Medical history and triplicate sitting blood pressure (BP) measurements were taken using validated automated upper-arm cuff devices. The data were uploaded to the international MMM cloud platform. Hypertension was defined as systolic BP ≥ 140 mm Hg and/or diastolic ≥90 mm Hg and/or self-reported use of drugs for hypertension. The same threshold was used to define uncontrolled BP in treated individuals. RESULTS: Data from 12,080 adults were collected (5,727/6,353 in MMM 2019/2022; men 46/49%, p < 0.01; mean age 52.7 ± 16.6/54.8 ± 16.2, p < 0.001; smokers, 24.7/30.5, p < 0.001; diabetics 12/11.5%, p = NS; cardiovascular disease 5/5.8%, p = NS). The prevalence of hypertension was 41.6/42.6% (MMM 2019/2022, p = NS), with 21.3/27.5% of individuals with hypertension being unaware of their condition (p < 0.001), 5.6/2.4% aware untreated (p < 0.001), 24.8/22.1% treated uncontrolled (p < 0.05), and 48.3/47.8% treated controlled (p = NS). CONCLUSION: In Greece, the COVID-19 pandemic did not appear to affect the prevalence and control of hypertension; however, the rate of undiagnosed hypertension was higher after the pandemic. National strategies need to be implemented for the early detection and optimal management of hypertension in the general population in Greece.

Opportunistic screening for hypertension: what does it say about the true epidemiology?

This study aimed to assess the reliability of opportunistic screening programs in estimating the prevalence, treatment, and control rate of hypertension in the general population. Two recent epidemiological surveys obtained data on hypertension in the adult general population in Greece. The EMENO (2013-2016) applied a multi-stage stratified random sampling method to collect nationwide data. The MMM (2019) collected data through opportunistic (voluntary) screening in five large cities. Hypertension was defined as blood pressure (BP) ≥ 140/90 mmHg (single occasion; average of 2nd-3rd measurement; electronic devices) and/or use of antihypertensive drugs. Data from a total of 10,426 adults were analyzed (EMENO 4,699; MMM 5,727). Mean age (SD) was 49.2 (18.6)/52.7 (16.6) years (EMENO/MMM, p < 0.001), men 48.6/46.5% (p < 0.05) and body mass index 28.2 (5.7)/27.1 (5.0) kg/m2 (p < 0.001). The prevalence of hypertension in ΕΜΕΝΟ/MMM was 39.6/41.6% (p < 0.05) and was higher in men (42.7/50.9%, p < 0.001) than in women (36.5/33.6%, p < 0.05). Among hypertensive subjects, unaware were 31.8/21.3% (EMENO/MMM, p < 0.001), aware untreated 2.7/5.6% (p < 0.001), treated uncontrolled 35.1/24.8% (p < 0.001), and treated controlled 30.5/48.3% (p < 0.001). In conclusion, the prevalence of hypertension was similar with random sampling (EMENO) and opportunistic screening (MMM). However, opportunistic screening underestimated the prevalence of undiagnosed hypertension and overestimated the rate of hypertension treatment and control. Thus, random sampling national epidemiological studies are necessary for assessing the epidemiology of hypertension. Screening programs are useful for increasing awareness of hypertension in the general population, yet the generalization of such findings should be interpreted with caution.

Statistical Mechanics of Non-Muscle Myosin IIA in Human Bone Marrow-Derived Mesenchymal Stromal Cells Seeded in a Collagen Scaffold: A Thermodynamic Near-Equilibrium Linear System Modified by the Tripeptide Arg-Gly-Asp (RGD).

Mesenchymal stromal cells (MSCs) were obtained from human bone marrow and amplified in cultures supplemented with human platelet lysate. Once semi-confluent, cells were seeded in solid collagen scaffolds that were rapidly colonized by the cells generating a 3D cell scaffold. Here, they acquired a myofibroblast phenotype and when exposed to appropriate chemical stimulus, developed tension and cell shortening, similar to those of striated and smooth muscle cells. Myofibroblasts contained a molecular motor-the non-muscle myosin type IIA (NMMIIA) whose crossbridge (CB) kinetics are dramatically slow compared with striated and smooth muscle myosins. Huxley's equations were used to determine the molecular mechanical properties of NMMIIA. Thank to the great number of NMMIIA molecules, we determined the statistical mechanics (SM) of MSCs, using the grand canonical ensemble which made it possible to calculate various thermodynamic entities such as the chemical affinity, statistical entropy, internal energy, thermodynamic flow, thermodynamic force, and entropy production rate. The linear relationship observed between the thermodynamic force and the thermodynamic flow allowed to establish that MSC-laden in collagen scaffolds were in a near-equilibrium stationary state (affinity ≪ RT), MSCs were also seeded in solid collagen scaffolds functionalized with the tripeptide Arg-Gly-Asp (RGD). This induced major changes in NMMIIA SM particularly by increasing the rate of entropy production. In conclusion, collagen scaffolds laden with MSCs can be viewed as a non-muscle contractile bioengineered tissue operating in a near-equilibrium linear regime, whose SM could be substantially modified by the RGD peptide.

Statistical Mechanics of the Human Placenta: A Stationary State of a Near-Equilibrium System in a Linear Regime.

All near-equilibrium systems under linear regime evolve to stationary states in which there is constant entropy production rate. In an open chemical system that exchanges matter and energy with the exterior, we can identify both the energy and entropy flows associated with the exchange of matter and energy. This can be achieved by applying statistical mechanics (SM), which links the microscopic properties of a system to its bulk properties. In the case of contractile tissues such as human placenta, Huxley's equations offer a phenomenological formalism for applying SM. SM was investigated in human placental stem villi (PSV) (n = 40). PSV were stimulated by means of KCl exposure (n = 20) and tetanic electrical stimulation (n = 20). This made it possible to determine statistical entropy (S), internal energy (E), affinity (A), thermodynamic force (A / T) (T: temperature), thermodynamic flow (v) and entropy production rate (A / T x v). We found that PSV operated near equilibrium, i.e., A ≺≺ 2500 J/mol and in a stationary linear regime, i.e., (A / T) varied linearly with v. As v was dramatically low, entropy production rate which quantified irreversibility of chemical processes appeared to be the lowest ever observed in any contractile system.

Ultraslow myosin molecular motors of placental contractile stem villi in humans.

Human placental stem villi (PSV) present contractile properties. In vitro mechanics were investigated in 40 human PSV. Contraction of PSV was induced by both KCl exposure (n = 20) and electrical tetanic stimulation (n = 20). Isotonic contractions were registered at several load levels ranging from zero-load up to isometric load. The tension-velocity relationship was found to be hyperbolic. This made it possible to apply the A. Huxley formalism for determining the rate constants for myosin cross-bridge (CB) attachment and detachment, CB single force, catalytic constant, myosin content, and maximum myosin ATPase activity. These molecular characteristics of myosin CBs did not differ under either KCl exposure or tetanus. A comparative approach was established from studies previously published in the literature and driven by mean of a similar method. As compared to that described in mammalian striated muscles, we showed that in human PSV, myosin CB rate constants for attachment and detachment were about 103 times lower whereas myosin ATPase activity was 105 times lower. Up to now, CB kinetics of contractile cells arranged along the long axis of the placental sheath appeared to be the slowest ever observed in any mammalian contractile tissue.

Comparative statistical mechanics of myosin molecular motors in rat heart, diaphragm and tracheal smooth muscle.

PURPOSE: Statistical mechanics establishes a link between microscopic properties of matter and its bulk properties. A. Huxley's equations (1957) [1] provide the necessary phenomenological formalism to use statistical mechanics. METHODS: We compared statistical mechanics in rat diaphragm in tetanus (tet; n=10) and twitch (tw; n=12) modes, in heart in twitch mode (n=20), and in tracheal smooth muscle in tetanus mode (TSM; n=10). This powerful tool makes it possible to determine: (i) statistical entropy (S) which is related to the dispersal of energy and represents a measure of the degree of disorder in muscular system; (ii) thermodynamic force A/T (chemical affinity A and temperature T); (iii) thermodynamic flow (υ); (iv) entropy production rate (A/T×υ), which quantifies irreversible chemical processes generated by myosin crossbridge (CB) molecular motors. RESULTS: All muscles studied operated near equilibrium, i.e., A<<2500J/mol and in a stationary linear regime, i.e., A/T varied linearly with υ. The heart operated farther from equilibrium than both diaphragm (tet and tw) and TSM, as attested by its high entropy production rate. S was of the same order of magnitude in heart and TSM but lower in diaphragm (tet and tw). CONCLUSION: CB kinetics derived from A. Huxley's equations conferred a characteristic profile in terms of statistical mechanics on each muscle type. All studied muscles differed in terms of statistical entropy, chemical affinity, and entropy production rate. Stimulation mode (tet and tw) modulated CB kinetics and statistical mechanics. All muscle types operated near equilibrium and in a stationary linear regime.