Cardio-respiratory system Kim Hastings – November 2010

Session aims To continue with the cardiac cycle Introduce respiratory system

Recap on last week Structure of heart – 4 chambers – 4 sets of valves – Key blood vessels Blood flow and vessels – Systemic and pulmonary circuit – Arteries, arterioles, capillaries, venules, veins Electrical conduction system and activity – ECG waves

More re-cap! Cardiac cycle – 4 phases – Systole and diastole – Pressure differences and consequences – Ventricular volume (SV, ESV and EDV) – Cardiac output (CO) – Regulation of CO – Affecting factors

Continuous Blood Flow During Cardiac Cycle – Aorta (and large arteries)—elastic Pressure reservoir – Store energy during systole as walls expand – Release energy during diastole as walls recoil inward – Maintains blood flow through entire cardiac cycle

Ventricular Volume – EDV = end-diastolic volume, volume of blood in ventricle at the end of diastole – ESV = end-systolic volume, volume of blood in ventricle at the end of systole – SV = stroke volume, volume of blood ejected from ventricle each cycle. – SV = EDV –ESV

Stroke Volume Volume of blood ejected by the ventricle each beat Stroke volume = end-diastolic volume – end-systolic volume = 130 mL – 60 mL = 70 mL

Heart Sounds – Due to ___________ flow when valves close – First heart sound Soft lubb AV valves close simultaneously – Second heart sound Louder dubb Semilunar valves close simultaneously

ECG and Mechanical Events – ECG = measure of _____________ events – Electrical events cause mechanical events, so precede mechanical events __________precedes atrial contraction _____ complex precedes ventricular contraction ____wave precedes ventricular relaxation

Cardiac Output Volume of blood pumped by each ventricle per minute – Cardiac output: CO = SV  HR – Average CO = 5 litres/min at rest – Average blood volume = 5.5 litres

Regulation of Cardiac Output – Regulate heart rate and stroke volume – Extrinsic and intrinsic regulation Extrinsic—neural and hormonal Intrinsic—auto-regulation

Heart Rate — Determined by SA Node Firing Rate – SA node intrinsic firing rate = 100/min No extrinsic control on heart, HR = 100 – SA node under control of ANS and hormones Rest: ____________ dominates, HR = 75 Excitement: ____________ takes over, HR increases

Factors Affecting Cardiac Output: Stroke Volume Primary factors affecting stroke volume – Ventricular contractility – Pre-load (End-diastolic volume) – After-load

Stroke Volume – Ventricles never completely empty of blood More forceful contraction will expel more blood – Extrinsic controls of SV Sympathetic drive to ventricular muscle fibres Hormonal control

Extrinsic Control of Stroke Volume – Sympathetic innervation of contractile cells Increases cardiac contractility – Parasympathetic innervation of contractile cells Not significant – Hormones Thyroid hormones, insulin, and glucagon increase force of contraction ______________________

Principle of Frank-Starling’s Law – Increased EDV stretches muscle fibres – Fibres closer to optimum length – Optimum length = greater strength of contraction – Result = increased SV

Intrinsic Control — Frank-Starling’s Law Increase venous return Increase strength of contraction Increase stroke volume

Factors Affecting End-Diastolic Volume – End-diastolic pressure = preload Filling time Atrial pressure Central venous pressure – After-load = pressure in aorta during ejection

FACTORS AFFECTING STROKE VOLUME

FACTORS AFFECTING CARDIAC OUTPUT

Summary of CO YouTube - The Physiology of Cardiac Output

Respiratory system – Internal respiration Oxidative phosphorylation – External respiration Exchange of oxygen and carbon dioxide between atmosphere and body tissues YouTube - Respiration 3D Medical Animation

External Respiration – Pulmonary ventilation – Exchange between lungs and blood – Transportation in blood – Exchange between blood and body tissues

External Respiration

Internal Respiration

Anatomy of the Respiratory System Upper airways Respiratory tract Structures of the thoracic cavity

Copyright © 2011 Pearson Education, Inc. Anatomy of the upper airways and the respiratory tract Nasal cavity Oral cavity Pharynx Epiglottis Larynx Upper airways Respiratory tract Oesophagus Left lungRight lung Alveolar sac Respiratory bronchioles Terminal bronchiole Terminal bronchioles Alveoli Glottis Trachea Primary bronchi Secondary bronchi Tertiary bronchi Diaphragm Cartilage rings

Functions of the Conducting Zone – Air passageway 150 mL volume = dead space volume – Increase air temperature to body temperature – Humidify air

Function of the Respiratory Zone – Exchange of gases between air and blood – Mechanism is by ____________

Anatomy of the Respiratory Zone

Alveoli – Alveoli = site of gas exchange – 300 million alveoli in the lungs (tennis court size) – Rich blood supply—capillaries form sheet over alveoli – Alveolar pores

Anatomy of the Respiratory Zone

Blood Supply to the Lungs

Structures of the Thoracic Cavity – Chest wall—air tight, protects lungs Rib cage Sternum Thoracic vertebrae Muscles—internal and external intercostals, diaphragm

Structures of the Thoracic Cavity – Pleura—membrane lining of lungs and chest wall Pleural sac around each lung Intrapleural space filled with intrapleural fluid – Volume = 15 mL

Chest Wall and Pleural Sac

Role of Pressure in Pulmonary Ventilation – Air moves in and out of lungs by bulk flow – Pressure gradient drives flow Air moves from high to low pressure Inspiration—pressure in lungs less than atmosphere Expiration—pressure in lungs greater than atmosphere

Pulmonary Ventilation Process where gas exchanged between atmosphere and alveoli. Air flow occurs due to pressure differences. Rate of flow influenced by compliance of lungs and airway resistance.

Pressure Changes During PV 1 Inspiration: Pressure in alveoli = < atmosphere Occurs by ________ lung volume Inverse relationship = Boyles Law Changes in lung volume = pressure changes Air forced in/out lungs = inhale/exhale Animation

Pressure Changes During PV 2 Expiration Occurs due to pressure _______________ Lung pressure > atmosphere Normal expiration = passive process Exercise = active process – muscles

Muscles of Respiration – Inspiratory muscles increase volume of thoracic cavity Diaphragm External intercostals – Expiratory muscles decrease volume of thoracic cavity Internal intercostals Abdominal muscles

Muscles of Breathing

Expiration – Expiration normally a passive process When inspiratory muscles stop contracting, recoil of lungs and chest wall to original positions decreases volume of thoracic cavity – Active expiration requires expiratory muscles Contraction of expiratory muscles creates greater and faster decrease in volume of thoracic cavity

Overview of Pulmonary Circulation – Arterial blood O 2 and CO 2 levels remain relatively constant Oxygen moves from alveoli to blood at same rate it is consumed by cells Carbon dioxide moves from blood to alveoli at same rate it is produced by cells

O 2 and CO 2 Movement

Respiratory Membrane

Gas Mixtures – Many gases are mixtures of different molecules – Partial pressure of a gas = proportion of pressure of entire gas that is due to presence of the individual gas – P total = P 1 + P 2 + P 3 + … P n

Gas Composition of Air – Composition of air 79% Nitrogen 21% Oxygen Trace amounts carbon dioxide, helium, argon, etc. Water can be a factor depending on humidity

Gas Composition of Air – P air = 760 mm Hg = P N 2 + P O 2 P N 2 = 0.79 x 760 mm Hg = 600 mm Hg P O 2 = 0.21 x 760 mm Hg = 160 mm Hg Air is only 0.03% carbon dioxide – P CO 2 = x 760 mm Hg = 0.23 mm Hg

Exchange of Oxygen and Carbon Dioxide – Gas exchange in the lungs – Gas exchange in respiring tissue

Diffusion of Gases – Gases diffuse down pressure gradients High pressure  low pressure – In gas mixtures, gases diffuse down partial pressure gradients High partial pressure  low partial pressure – A particular gas diffuses down its own partial pressure gradient Presence of other gases irrelevant

O 2 and CO 2 Partial Pressures

Gas Exchange in Respiring Tissue – Gases diffuse down partial pressure gradients – P O 2 cells  40 mm Hg ; P O 2 systemic arteries =100 mmHg Oxygen diffuses from blood to cells P O 2 systemic veins = 40 mm Hg – P CO 2 cells  46 mm Hg ; P CO 2 systemic arteries = 40 mmHg Carbon dioxide diffuses from cells to blood P CO 2 systemic veins = 46 mm Hg Animation: Changes in the Partial Pressures of Oxygen and Carbon Dioxide Animation: Changes in the Partial Pressures of Oxygen and Carbon Dioxide

Mixed Venous Blood – Actual amount of oxygen and carbon dioxide that is exchanged in any given vascular bed depends on metabolic activity of tissue Greater rate of metabolism  _________ exchange – P O 2 and P CO 2 in different systemic veins vary

Mixed Venous Blood – All systemic venous blood returns to right atrium and pumped out right ventricle into pulmonary artery – Blood in pulmonary artery = mixed venous blood P O 2 = 40 mm Hg P CO 2 = 46 mm Hg

Airway Resistance – As airways get smaller in diameter they increase in number, keeping overall resistance low – Pressure gradient needed for air flow thus low ~1 mm Hg – An increase in resistance makes it harder to breathe Pressure gradient needed for air flow > 1 mm Hg

Pathological States That Increase Airway Resistance – Asthma Caused by spastic contractions of bronchiolar smooth muscle – Chronic obstructive pulmonary diseases COPD

Clinical Significance of Respiratory Volumes and Air Flows – Lung volumes and capacities – Pulmonary function tests

Spirometry Measurements

Obstructive Pulmonary Diseases – Associated with increased airway resistance – Residual volume increases (harder to expire) – Functional residual capacity increases – Vital capacity decreases – Major obstructive pulmonary diseases COPD (chronic bronchitis and emphysema) Asthma

Pulmonary Function Tests: Forced Vital Capacity (FVC) Maximum volume inhale followed by exhale as fast as possible – Low FVC indicates restrictive pulmonary disease More difficult for lungs to expand Total lung capacity decreases Vital capacity decreases

Pulmonary Function Tests: Forced Expiratory Volume (FEV) Percentage of FVC that can be exhaled within certain time frame – FEV 1 = percent of FVC that can be exhaled within 1 second – Normal FEV 1 = 80% If FVC = 4000 ml, should expire 3200 ml in 1 sec FEV 1 < 80% indicates obstructive pulmonary disease

Minute Ventilation Total volume of air entering and leaving respiratory system each minute – Minute ventilation = V T  RR – Normal respiration rate = 12 breaths/min – Normal V T = 500 mL – Normal minute ventilation = 500 mL  12 breaths/min = 6000 mL/min

Anatomical Dead Space – Air in conducting zone does not participate in gas exchange – Thus, conducting zone = anatomical dead space – Dead space approximately 150 mL

Summary Cardiac output complete Factors affecting stroke volume Respiratory system – Key structures – Gaseous exchange – Key lung volumes and capacities – Lung function tests