Basic concepts of polysomnography channels
Ravi Gupta, S. R. Pandi Perumal, Ahmed S. BaHammam in Clinical Atlas of Polysomnography, 2018
An ECG depicts the sum of the electrical activity of the heart during its pumping process. The heart has its own conduction system that is present below the endocardium. The conduction system of the heart is specialized where impulses generated in the sino-atrial (SA) node traverse down to the atrioventricular (AV) node and then to the ventricles. Upon activation of the conduction system, changes akin to the skeletal muscles occur that result in contraction and relaxation. The heart has four chambers, two atria, and two ventricles. They do not contract together. First, the conduction system depolarizes the atria (when the ventricles remain at resting membrane potential), and after a few seconds, a depolarization wave proceeds to the ventricles (by that time atria reaches the resting membrane potential). When the atria depolarize, their outer surface becomes positive compared to the ventricles. Hence, a dipole is created and current flows from the right side (because ventricles are on the left side as compared to atria) and also from the backside of the chest to front (because atria are close to back while ventricles are closer to the anterior chest wall). Localized change in the membrane potential of the heart with reference to the other part creates a dipole (which keeps changing temporally) that can be picked up by surface electrodes during an ECG. The direction of waveforms in the ECG depends upon the lead used. For example, bipolar lead attached to the right arm and left arm, with the negative pole of the channel to the right side and the positive towards the left side. Since the current from the heart is flowing from right to left, it will create a positive deflection in this lead and will be observed as the first half of the P wave in the ECG. The second half of the P wave reflects that action potentials in the atrial muscles are coming back to the resting membrane potential. In this manner, because of the changing dipoles in the heart, QRS complex and T waves are generated.
Overview of the cardiovascular system
Neil Herring, David J. Paterson in Levick's Introduction to Cardiovascular Physiology, 2018
The heart consists of two synchronous, muscular pumps, the right and left ventricles (Figure 1.4). Each pump is filled from a contractile reservoir, the right or left atrium. The right ventricle pumps deoxygenated blood through the pulmonary trunk to the lungs (Figure 1.5). Four pulmonary veins return oxygenated blood from the lungs to the left side of the heart, completing the short, low-pressure pulmonary circulation. The left ventricle pumps an equal volume of oxygenated blood to the tissues of the body. The tissues extract some of the O, and the partly deoxygenated blood returns via two great veins, the superior and inferior vena cava, to the right atrium. This completes the long, high-pressure systemic circulation. One-way valves in the heart and veins ensure that blood follows the circular pathway described earlier, as first demonstrated by the physician William Harvey. Harvey’s originality and groundbreaking introduction of experimentation into physiology and medicine disproved the earlier ebb-and-flow dogma of the previous 1000 years. His elegant work is delightfully described in his book De Motu Cordis (trans. Concerning the Motion of the Heart, 1628).
The transport and exchange systems: respiratory and cardiovascular
Nick Draper, Helen Marshall in Exercise Physiology, 2014
As was mentioned earlier the heart is comprised of two pumps. The heart’s double pump can be thought of in two ways. Firstly, deoxygenated blood pumped into the right ventricle supplies blood to the lungs and the left side supplies oxygenated blood to systemic circulation. Secondly, the heart contracts in a ‘1–2’fashion, which can be inferred from the sounds heard when using Doppler ultrasound echocardiography (which makes it possible to listen to the sounds of the heart). During echocar-diography the contraction of the heart appears as a ‘lub-dup’ sound. The ‘1’or ‘lub’, the first sound, is created by the closure of the atrioventricular valves at the start of a ventricular contraction (after completion of atrial contraction) and the ‘2’, or dup phase of contraction, represents the end of the ventricular contraction and the closure of the semi-lunar valves in the pulmonary trunk and aorta, which stop blood flowing back into the ventricles (after which the atria will begin to contract again to fill the ventricles).
Prognostic significance of third ventricle dilation in spontaneous intracerebral hemorrhage: a preliminary clinical study
Published in Neurological Research, 2008
Ozgur Ozdemir, Tarkan Calisaneller, Askin Hastürk, Fatih Aydemir, Hakan Caner, Nur Altinors
Objective: Although numerous factors have been described that predict outcome after spontaneous intracerebral hemorrhage (ICH), very little is know about the role of hemorrhagic dilation of the third ventricle in development of hydrocephalus and prognosis. The objective of this study was to investigate whether the presence of hemorrhagic third ventricle dilation after ICH would predict development of hydrocephalus and outcome. Methods: We identified the patients with spontaneous ICH treated with external ventricular drainage (EVD) in this retrospective study. Computerized tomography (CT) was performed at admission within 24 hours of onset and retrospectively analysed to determine lesion size and location, status of third and fourth ventricle and frontal horn index (FHI). Glasgow coma scale (GCS) score, mean arterial pressure (MAP), etiology and demographic data were obtained from medical records. Outcome was determined using modified Rankin score at month 3. Patients with and without third ventricle dilation were compared in terms of hydrocephalus (FHI>0.38), initial GCS score, age and MAP, and analyses were performed to determine whether third ventricle dilation was a predictor of poor outcome. Results: Of the 22 patients studied, all had thalamic or basal ganglia hemorrhage with intraventricular hemorrhage (IVH) and all are treated with external ventricular drainage (EVD). Of the 22 patients, 12 had third ventricle dilation (width≥10 mm) and ten patients had non-dilated third ventricle (width<10 mm). Patients with third ventricle dilation had lower GCS scores (7.4 ± 1.8 versus 9.7 ± 2.1, p<0.005) and had higher FHI (0.46 ± 0.06 versus 0.38 ± 0.02, p<0.005) as compared to patients with non-dilated third ventricle. The differences in age (59.5 ± 9.4 versus 59.2 ± 11.2) and MAP (128.3 ± 16.0 versus 130.5 ± 13.6) of the patients were not significant statistically. Sixty-six percent of patients (8/12) with third ventricle dilation and 60% of patients (6/10) with normal third ventricle were dead 6 months post-operation and mortality rate did not differ significantly. Discussion: Although the roles of various factors are well described in the prognosis of spontaneous ICH, little is known about the role of third ventricle dilation. Based on our results, we concluded that third ventricle dilation is a poor prognostic factor.
Shape and Shift of the Laryngeal Ventricle During Phonation
Published in Acta Oto-Laryngologica, 1967
The shape and shift of the laryngeal ventricle during phonation was studied in profile roentgenographs of 41 young males with normal voice function. None of them was a trained singer. From a mean of 14 mm at rest position of the vocal folds and during quiet respiration, the laryngeal ventricle was elongated by about 7 mm when the tone frequency was increased to 325 cps. The height of the laryngeal ventricle was increased from about 3 mm at rest position to about 5 mm at 225 cps. On further increase of the tone frequency the height diminished. During respiration the laryngeal ventricle was generally located at the level of the lower border of the 5th cervical vertebra. During phonation at high pitch the laryngeal ventricle was generally elevated while at low pitch it moved downwards. The elongation of the laryngeal ventricle was due mainly to a forward movement of the anterior border of the ventricle whereas the distance between the posterior border and the cervical column remained unchanged. It is confirmed that during phonation at increasing pitch the cricoid arch is rotated upwards about the transverse axis through the cricothyroid joints. The thyroid cartilage is moved forwards at the same time as the level of the laryngeal ventricle is raised.
Detection of Early Cardiac Dysfunction in Patients with β-Thalassemia Major and Thalassemia Trait by Tissue Doppler Echocardiography
Published in Pediatric Hematology and Oncology, 2011
Yasemin Isik Balci, Dolunay Gurses
Cardiac complications are the leading cause of death in β-thalassemia major (TM) patients. The aim of this study was to investigate the impact of iron overload on ventricular functions using conventional and tissue Doppler imaging (TDI) in patients with TM and compare them with children with thalassemia trait (TT) and healthy controls. This prospective study includes 3 groups: group 1: 29 patients with β-TM; group 2: 28 patients with TT; group 3: 29 healthy controls. Peak late relaxation velocity determined by conventional echocardiography for the right ventricle was significantly higher and the E/A ratio for the right ventricle and left ventricle were significantly lower in TM patients than the other groups (P < .05). Peak late relaxation velocity determined by TDI for the left ventricle, interventricular septum, and right ventricle were significantly higher in TM patients than the TT subjects and controls (P < .001). The E/A ratio determined by TDI for the left ventricle, interventricular septum, and right ventricle were significantly lower in group 1 than the other 2 groups (P < .001). There was a negative correlation between the ferritin level and E/A ratio for the left ventricle, interventricular septum, and right ventricle using TDI (P < .05). Conventional echocardiographic techniques have failed to distinguish ventricular functions of asymptomatic patients with TM from the subjects with TT and from normal controls when global functions were examined. The present study indicates that TDI should be used for screening of TM and TT subjects’ cardiac functions.
Related Knowledge Centers
- Pulmonary Circulation
- Atrium
- Blood
- Right Ventricle
- Heart
- Interventricular Septum