Understanding Blood Pressure and Pulse

Blood Pressure and Pulse

• Systolic blood pressure is the maximum pressure exerted on artery walls during ventricular contraction.
• Diastolic blood pressure is the minimum pressure exerted on artery walls during ventricular relaxation.
• Blood pressure is measured using a sphygmomanometer, normal ranges are around 120/80 mmHg for adults.
• Mean arterial pressure (MAP) represents the average arterial pressure throughout one cardiac cycle.
• MAP is calculated as diastolic pressure plus one-third of the pulse pressure.
• Physiological factors determining blood pressure: cardiac output, blood volume, and vascular resistance.
• MAP is equal to diastolic pressure plus 1/3 of pulse pressure (PP).
• Pulse pressure (PP) is systolic pressure (SP) minus diastolic pressure (DP).
• A second equation for MAP is cardiac output (CO) multiplied by peripheral resistance (Rp).
• Cardiac output (CO) is heart rate (HR) multiplied by stroke volume (SV).
• Stroke volume (SV) is end-diastolic volume (EDV) minus end-systolic volume (ESV).

Respiratory Physiology

• Major structures of the upper respiratory tract include the nasal cavity, pharynx, and larynx. Major structures of the lower respiratory tract include the trachea, bronchi, and lungs.
• The nasal cavity conditions incoming air by warming, humidifying, and filtering it.
• Alveoli are the primary sites of gas exchange in the lungs; their structure supports this function by providing a large surface area and thin walls for diffusion.
• The diaphragm and intercostal muscles play a crucial role in ventilation by changing the volume of the thoracic cavity, creating pressure gradients that drive air in and out of the lungs.
• Inspiration is the process of drawing air into the lungs, it occurs when the diaphragm contracts and the rib cage expands, decreasing pressure in the lungs.
• Expiration is the process of expelling air from the lungs; it occurs when the diaphragm relaxes and the rib cage recoils, increasing pressure in the lungs.
• Tidal volume is the amount of air inhaled or exhaled during normal breathing. Inspiratory reserve volume is the maximum amount of additional air that can be inhaled after a normal inhalation. Expiratory reserve volume is the maximum amount of additional air that can be exhaled after a normal exhalation.
• Oxygen and carbon dioxide are exchanged at the alveoli and systemic tissues through diffusion. Oxygen moves from the alveoli into the blood, and carbon dioxide moves from the blood into the alveoli and from the tissues into the blood, and carbon dioxide moves from the blood into the tissues.
• Hemoglobin transports oxygen in the blood; factors influencing its affinity for oxygen include pH, temperature, and partial pressure of carbon dioxide.
• Most carbon dioxide is transported in the blood as bicarbonate ions.
• The pons and medulla oblongata play a vital role in respiratory control by regulating the rate and depth of breathing.
• Chemoreceptors regulate breathing rate and depth by detecting changes in blood pH, carbon dioxide, and oxygen levels.
• Restrictive lung diseases are characterized by a reduction in lung volume (e.g., pulmonary fibrosis), while obstructive lung diseases are characterized by airflow obstruction (e.g., asthma, COPD).
• Respiration involves flow from regions of higher to lower pressure.
• Pressure gradients are created by a muscular pump.
• Resistance affects flow in the respiratory system.
• The diameter of tubes in the respiratory system is a factor in flow.
• Components of the respiratory system include the conducting system or airways, alveoli, and bones/muscles of the thorax and abdomen.
• Alveoli (singular alveolus) serve as the site of gas exchange.
• According to Dalton's Law, total pressure equals the sum of all partial pressures (Pgas).
• As an example, air is 78% nitrogen with oxygen accounting for 21%.
• Gases move down a partial pressure gradient.
• Boyle's Law is represented by P₁V₁ = P₂V₂.
• A single respiratory cycle involves one inspiration followed by one expiration.
• Atmospheric pressure is around 760mm Hg.
• Total lung capacity (TLC) is the sum of inspiratory reserve volume (IRV), expiratory reserve volume (ERV), and tidal volume (VT).
• Air flow is proportional to the pressure difference (∆P) divided by resistance (R).
• Expiration can be passive or active.
• Inspiration occurs when alveolar pressure decreases.
• Expiration occurs when alveolar pressure increases.
• Compliance refers to the ability of the lungs to stretch.
• High compliance means the lungs stretch easily.
• Low compliance requires more force to stretch the lungs and is associated with restrictive lung diseases like fibrotic lung diseases (fibrosis) and inadequate surfactant production (NRDS).
• Elastance refers to the ability of the lungs to return to resting volume after a stretching force is released.
• Wider airways result in less resistance: R ∝ Lη/r⁴.
• Bronchoconstriction increases resistance (parasympathetic).
• Bronchodilation decreases resistance; beta 2 receptors on smooth muscles relax when epinephrine is present.

Key Functions of the Respiratory System

• The main function is gas exchange, transferring O₂ into the blood and removing CO₂
• The respiratory system provides oxygen for cellular respiration in mitochondria to generate ATP
• It regulates pH by exhaling CO₂, which influences blood pH levels
• Volatile wastes, such as water vapor and carbon dioxide, are removed
• Sound is produced through the vocal cords in the larynx
• The respiratory system helps regulate blood pressure by secreting angiotensin-converting enzyme (ACE)

Respiratory Anatomy and Epithelium

• The nasal cavity warms, filters, and humidifies incoming air
• The pharynx is lined with stratified squamous epithelium
• The larynx contains vocal cords and is involved in sound production
• Laryngitis is inflammation of the larynx
• The epiglottis prevents food from entering the trachea during swallowing.
• The trachea, made of C-shaped hyaline cartilage, is lined with pseudostratified ciliated columnar epithelium
• Cilia in the trachea move mucus and debris upward, opposing airflow
• Bronchioles lose cartilage and gain smooth muscle compared to bronchi
• Alveoli are the site of gas exchange in the lungs
• Alveoli contain simple squamous epithelium for rapid diffusion

Mechanics of Breathing

• Boyle's Law states that pressure is inversely related to volume
• During inspiration at rest, the diaphragm and external intercostals contract, increasing volume, decreasing pressure, and allowing air to flow in
• During expiration at rest, the diaphragm and intercostals relax, decreasing volume, increasing pressure, and allowing air to flow out
• Muscles assisting in forced inspiration: Sternocleidomastoid, scalenes, pectoralis major
• Muscles assisting in forced expiration: Abdominal muscles and internal intercostals

Nervous System Control

• The phrenic nerve stimulates the diaphragm
• The Dorsal Respiratory Group (DRG) controls quiet breathing
• The Ventral Respiratory Group (VRG) controls forced breathing
• The apneustic center in the pons stimulates the DRG to promote inspiration
• The pneumotaxic center inhibits the apneustic center to allow expiration

Gas Exchange and Transport

• 98% of oxygen is transported bound to hemoglobin, 2% dissolved in plasma
• Carbon dioxide is transported 70% as bicarbonate, 23% bound to hemoglobin, and 7% dissolved in plasma
• Carbonic anhydrase helps convert CO₂ into bicarbonate
• The chloride shift involves the exchange of Cl⁻ for HCO₃⁻ to maintain electrostatic neutrality in RBCs

Respiratory Volumes and Capacities

• Tidal Volume (TV): Normal breath is ~500 mL
• Inspiratory Reserve Volume (IRV): Volume after forced inhale is ~3100 mL
• Expiratory Reserve Volume (ERV): Volume after forced exhale is ~1200 mL
• Residual Volume (RV): Air remaining after maximal exhale is ~1200 mL
• Vital Capacity (VC): VC = TV + IRV + ERV
• Inspiratory Capacity (IC): IC = TV + IRV
• Functional Residual Capacity (FRC): FRC = ERV + RV
• Total Lung Capacity (TLC): TLC = TV + IRV + ERV + RV
• The efficiency of breathing is determined by the rate and depth of breathing.
• Total pulmonary ventilation equals ventilation rate multiplied by tidal volume.
• Alveolar ventilation is calculated by ventilation rate multiplied by (tidal volume - dead space).
• Regulation of arteriole and bronchiole diameters helps match ventilation and blood flow.

Respiratory Conditions

• Pharyngitis is inflammation of the pharynx (sore throat)
• Laryngitis is inflammation of the larynx (loss of voice)
• Asthma is reversible airway constriction
• COPD is chronic airflow obstruction, including emphysema and chronic bronchitis
• Emphysema involves alveolar destruction and increased lung compliance
• Pulmonary edema is fluid in alveoli, increasing diffusion distance

Auscultation – Lung Sounds

• Wheezes: High-pitched sounds from narrowed airways
• Stridor: Harsh sound from upper airway obstruction
• Crackles (rales): Sounds from fluid in alveoli
• Pleural friction rub: Sound from inflamed pleural surfaces rubbing together
• Auscultation is a diagnostic technique for obstructive lung diseases.
• Asthma involves the contraction of small mm bronchioles.
• Obstructive sleep apnea includes intermittent airflow blockage during sleep.
• Emphysema is characterized by a reduced or destroyed respiratory membrane, leading to shortness of breath (SOB).
• Chronic bronchitis involves swelling of airways with cough and phlegm.
• COPD (chronic obstructive pulmonary disease) can occur if there is emphysema or chronic bronchitis.