Kussmaul respirations as a respiratory pattern may be associated with which characteristic(s)?

Diagnostic Terminology

A pH of less than 7.35 is called acidemia, while that over 7.45 is termed alkalemia. A PCO2 over 45 Torr indicates respiratory acidosis or hypercapnia, while values under 35 (males) or 30 (females) indicate respiratory alkalosis or hypocapnia. A standard base excess (SBE) more negative than − 2.5 mM is metabolic acidosis and over + 2.5 mM (these values may vary) is metabolic alkalosis. Presence of compensatory responses to chronic acid–base respiratory or metabolic imbalances can be predicted and used in diagnosis (Fig. 8).

A change of 1 mmHg in results in a 0.008 change in pH in the opposite direction (above and below PCO2 40 mmHg) while a reduction of 1 mEq in [HCO3 −] below 24 mEq/L will decrease the PCO2 with 1 mmHg. pH will change with approximately 0.15 units in the same direction for each 10 mEq/L change in [HCO3 −]. The relationship between pH and PCO2 can be used to determine whether the primary disorder is respiratory or metabolic. If the pH and PCO2 change in opposite directions then the disorder is likely to be respiratory and if it changes in the same direction the disorder is likely to be metabolic.

Normal PO2 at sea level in young adults is 90–100 mmHg. It falls with age to 60–70 mmHg at age 80. There is no consensus on what PO2 level is defined as ‘hypoxia’. Arterial oxyhemoglobin ‘functional’ saturation (100 x HbO2/[HbO2 + HHb]) is normally 97–98% (i.e., 2–3% deoxyhemoglobin, HHb). Carboxyhemoglobin or methemoglobin or other abnormal forms, if present, reduces ‘fractional’ saturation (or % oxyhemoglobin) computed as 100 × HbO2/total Hb but is not counted in ‘functional’ saturation. The terms ‘hypoxia’ or ‘hypoxemia’ generally imply that SaO2 is at least 5% lower than expected (at that age and altitude).

Breathing Patterns in the Normal Lung

As discussed above, the normal breathing pattern is somewhat difficult to define. Not surprisingly, normal breathing patterns predominate in normal lungs! However, abnormal breathing patterns can occur when the ultrastructure of the lung is completely intact which gives us some insight into the overall control of breathing (which will not be discussed in detail here).

Abnormal breathing patterns in the normal lung can be divided into physiological and pathological (Fig. 2). A number of physiological causes of abnormal breathing patterns occur in the normal lung such as during vigorous exercise, in anxiety, and when body core temperature is raised and in many cases they may go unnoticed by the individual. However, at the extremes of these various causes, it is well recognized that respiratory frequency and depth are increased, leading to air-hunger and the sensation of breathlessness. In extreme cases of anxiety and some functional disorders, hyperventilation may occur which promotes increased carbon dioxide excretion, and the development of a respiratory alkalosis. This often leads to a further change in breathing pattern where patients complain of variable dyspnea, the sensation that it is easier to breathe in than out. Light-headedness, paresthesiae, tetany, chest pain, and a feeling of impending collapse can also accompany the breathing pattern changes.

A number of specific breathing pattern abnormalities also occur in the normal lung, which accompany pathological conditions such as severe central nervous system and neuromuscular disease and also profound metabolic acidosis of both endogenous and exogenous etiologies.

Cheyne-Stokes breathing pattern was described by Scottish and Irish physicians in the 1800s. The pattern displays an abnormal rhythm, which is regularly irregular and is associated with a progressive increase in depth and often frequency of breathing. The pattern occurs over a 15–60 s cycle in a crescendo-decrescendo manner and is characterized by apneic episodes.

It is thought to result from a complex interplay of increased chemoreceptor hypercapnic ventilator response, reduced circulation time and reduced blood gas buffering ability. The combination of the above result in physiological “overshoot” in response to hyper and hypocapnoea, resulting in further over compensation and the classically described crescendo-decrescendo respiratory rate and tidal volumes.

It can be normal in some individuals during sleep but is always abnormal when it occurs while the subject is awake. Causes include aging, obesity, congestive heart failure, and neurologic disorders, for example, meningitis, infarction, or pontine hemorrhage.

Biot’s breathing pattern was described by a French physician and is a variant of Cheyne-Stokes. There is a succession of hyperpnea, hyperventilation, and apnea but the pattern is not regular and there is no crescendo-decrescendo phase. Causes include meningitis and medullary compression and it often precedes death, when it may deteriorate into agonal breathing.

Ataxic (agonal) breathing pattern occurs after brainstem damage and consists of continuous irregular shifts of hyperventilation, hypoventilation, and apnea in no particular succession (unlike the Biot’s and Cheyne-Stokes patterns). Apneustic breathing pattern is characterized by deep inspiration, followed by a postinspiratory breath hold and rapid exhalation. It generally signifies the presence of brainstem lesions usually at the level of the pons.

In the central hyperventilation breathing pattern, patients are very tachypneic and breathe extremely deeply, exhibiting profound air-hunger. This pattern is seen in midbrain/upper pontine lesions and is due to damage to the medullary respiratory center. It is a sinister pattern, described as fibrillation of the respiratory centers, which usually heralds impending death.

The Kussmaul breathing pattern is caused by severe metabolic acidosis, which can complicate endogenous diseases such as diabetic ketoacidosis and uremia and also exogenous conditions such as salicylate poisoning. It arises due to excessive stimulation of the respiratory center and is manifest by air-hunger and in severe cases can disturb the level of consciousness. Kussmaul breathing has similarities to the central hyperventilation pattern, as both cause dramatic changes in respiratory depth. Although both are associated with increases in the frequency of respiration, the latter pattern tends to have far greater effects on this parameter.

Finally, endogenous disorders such as hypothyroidism and exogenous toxins, particularly overindulgence of opioid narcotics, are frequently associated with bradypnea.

Response Limitations

When an individual has ostensibly exercised to the limit of tolerance, it is important to determine whether particular systems that contribute to the muscular energy production have reached their limit. For example, evidence of ventilatory system limitation is present if the V˙Eattained at the end of exercise (V˙Emax) (i.e. at the limit of tolerance) attains its maximally attainable value, typically estimated as the maximum voluntary ventilation (MVV) determined at rest (Fig. 3, right). That is, the individual has no “breathing reserve” (BR; defined as MVV − V˙Emax) (Fig. 5). The BR can be zero (or even negative in an individual who bronchodilates during exercise) either as a result of MVV being low (e.g. COPD patients) or MVV being normal but the achievable work rates and V˙Ebeing exceptionally high (highly-fit endurance athletes). Such limitation can also be viewed in the context of the expiratory flow-volume loop, an absence of flow reserve being evident when the spontaneous expiratory flow at a particular lung volume during exercise encroaches on the maximum-effort expiratory flow achievable at that lung volume at rest (Fig. 6). In addition, a lack of volume reserve during exercise is identified when VT impinges on the inspiratory capacity (IC), as in restrictive lung diseases. Thus, these ventilatory and volume maxima provide useful frames-of-reference for discriminating among potential causes of exercise limitation in the respiratory patient.

In contrast to healthy (especially young) individuals, the tolerable work rate range in patients with lung disease is constrained by a combination of pulmonary factors, chief of which are:

impaired pulmonary-mechanical and gas-exchange function, which increase the V˙Edemands;

limitations of airflow generation or lung distention;

increased physiological costs of meeting the V˙Edemands, in terms of respiratory-muscle work, perfusion and O2 consumption;

predisposition to shortness-of-breath or dyspnea, consequent to the high fraction of the achievable airflow or lung distention demanded by a particular work rate, and which is commonly exacerbated by arterial hypoxemia and early-onset metabolic acidosis; along with

conditions such as co-existent heart disease, pulmonary hypertension, nutritional deficiencies and detraining as a result of low-activity patterns of daily living—the latter helping explain the high incidence of “fatigue” rather than dyspnea as the dominant reported cause of exercise limitation in some COPD patients.

For example, in COPD patients, the increased airways resistance and/or decreased pulmonary recoil pressure reduces the maximum achievable expiratory airflow. This reduces the patient’s effective operating range of V˙Eduring exercise. The V˙Edemands, however, are commonly greater than normal, reflecting the high VD/VT (a component of which is also seen in the otherwise healthy elderly, as a result of loss of lung recoil). This leads to abnormally high values of V˙E/V˙O2and V˙E/V̇CO2, which may be increased further by arterial hypoxemia. However, some COPD patients can have higher-than-normal PaCO2 levels, especially those with poor peripheral chemosensitivity which constrains the ability to increase V˙Eappropriately. Thus, the combination of increased V˙Edemands and decreased maximum-attainable V˙Eleads to little or no BR or flow reserve at maximum exercise (Figs. 3, 5 and 6).

Some COPD patients may generate spontaneous expiratory airflows during exercise which not only equal, but actually exceed, those achieved at a given lung volume during a maximal flow-volume maneuver (Fig. 6). The seeming paradox of expiratory airflow during exercise exceeding that generated during a maximal expiratory effort at rest can be explained by:

Bronchodilatation from exercise-induced increases in circulating catecholamines;

The forced-expiratory maneuver from total lung capacity allowing lung units with fast mechanical τ’s (i.e. the product of airways resistance and thoracic compliance) to empty at high lung volumes, leaving the lung units with longer τ’s to empty at lower lung volumes. When these less-than-maximum lung volumes are attained during spontaneous breathing, the fast-τ units are recruited at these lower lung volumes, resulting in greater airflow—at that lung volume; and

Maximum expiratory airflow not being achieved with maximum expiratory effort (especially at low lung volumes) because of dynamic airway compression, and even closure in some cases, during the forced maneuver.

An important functional consequence of lung units having longer-than-normal mechanical τ values is that the time available for lung emptying becomes increasingly challenged with increasing work rate, as expiratory duration shortens progressively. Thus, COPD patients characteristically demonstrate “dynamic hyperinflation” during exercise, with end-expiratory lung volume (EELV) increasing (rather than the normal decrease) (Fig. 6). This results in the VT encroaching upon the compliance limits, adding a “restriction-like” component to the obstruction. Factors which reduce breathing frequency (fB) during exercise, such as the breathing of O2-enriched air and/or exercise training can prove effective at reducing the hyperinflation and therefore improving exercise tolerance. Dynamic hyperinflation can be tracked during incremental exercise by having patients perform IC maneuvers at regular intervals to assess changes in EELV (with the assumption that total lung capacity does not change during the exercise).

As the upper limit for exercise tolerance in COPD patients is typically set by pulmonary determinants, other components of the body’s energy supply systems may not be stressed to their limits. Consequently, maximum heart rate (HR), O2-pulse (V˙O2/HR) and [L−]a are often markedly less than predicted. And as maximum HR does not attain the patient’s age-predicted maximum (averaging ∼ 220—age, but with a large standard deviation of ∼ 10 min− 1), there can be an appreciable heart rate reserve at maximum exercise. Although the pattern of blood-gas response to exercise is highly variable in COPD patients, in many cases the resting levels of PaO2 can be maintained during exercise without further hypoxemia: diffusion limitation across the alveolar-capillary bed does not seem to be significantly contributory and the increased V˙A/Q̇dispersion does not appear to worsen. Also, those patients who are capable of generating a metabolic acidosis during exercise usually evidence little or no respiratory compensation owing to the obstructive constraint.

In patients with restrictive lung diseases, such as diffuse interstitial fibrosis, reduced airflow generation (at a particular lung volume) is not of concern. Rather, the increased pulmonary elastance demands greater inspiratory muscle force and increased work of breathing. This predisposes the restrictive patient to tachypnea (fB > 50 min− 1 being common at maximum exercise), with VT often reaching the reduced IC. Unlike COPD, however, the hypoxemia in these patients typically worsens as WR increases—not, it seems, because of further-impaired V˙A/Q̇matching but because of increasing diffusion limitation, often leading to (A − a)PO2 in excess of 60 mmHg at the limit of tolerance.

While exercise does not usually worsen the degree of airway obstruction in the emphysematous and/or and bronchitic forms of COPD, it typically does in patients with asthma. Although the exercise-induced bronchoconstriction—which can also occur in individuals with no history (or even a recognition) of airway hyperreactivity—is sometimes manifest during exercise, it is most typically a post-exercise phenomenon, with high-intensity exercise the more potent trigger. A prior moderate-intensity warm-up can ameliorate the degree of bronchoconstriction during a subsequent high–intensity exercise bout, as does—for a short period—a prior exercise-induced bronchospastic episode itself.

Dyspnea

Dyspnea is the term applied to sensations experienced by individuals who complain of uncomfortable respiratory sensations. Dyspnea has been defined in several ways, for example, ‘difficult, labored, uncomfortable breathing,’ an ‘awareness of respiratory distress,’ ‘the sensation of feeling breathless or experiencing air hunger,’ and ‘an uncomfortable sensation of breathing.’ The sensation of dyspnea derives from interactions among multiple physiological and behavioral responses. It is the result of an imbalance between ventilatory demand and capacity due to increased work of breathing. Often, the patient has attributed the insidious onset of breathlessness to aging, deconditioning, obesity, or a recent upper respiratory tract illness. Some patients deny the presence of dyspnea even when questioned because they perform a limited amount of activity and so do not ‘experience’ any significant discomfort. Occasionally a spouse or friend brings the problem to their attention. It is important to determine the duration and extent of dyspnea, cough, and sputum production (if any). The dyspnea history should focus on onset and timing of symptoms, the patient’s position at onset of symptoms, the relationship of symptoms to activity, and any factors that may improve or exacerbate symptoms. In most cases, the primary problem is heart, lung, or neuromuscular abnormalities, which can be identified largely by the history and physical examination. The quality of breathing discomfort often provides tips to the underlying diagnosis; the absence of cigarette smoking or exposure to biomass fuel smoke is strongly against a diagnosis of COPD. The occupational history may lead to a diagnosis of asbestosis or hypersensitivity pneumonitis. The presence of reproducible events such as exposure to fumes or cold air is common with airways hyperreactivity. When developing a differential diagnosis, it is useful to attempt to distinguish respiratory causes of dyspnea from cardiovascular dyspnea. It is not uncommon for a patient to have more than one problem contributing to the breathing discomfort. Diagnostic testing commonly follows to identify the specific nature of the disorder. Dyspnea is classified into the following categories: (1) Acute dyspnea has a short list of causes, most of which are readily identified: asthma, pulmonary infection, pulmonary edema, pneumothorax, pulmonary embolus, metabolic acidosis, or acute respiratory distress syndrome (ARDS). (2) Nocturnal dyspnea suggests asthma, gastroesophageal reflux disease (GERD), left ventricular dysfunction, or obstructive sleep apnea. (3) Orthopnoea (dyspnea on recumbency) is typically caused by fluid overload in the lungs caused by left ventricular dysfunction. However, it may also be caused by diaphragmatic weakness, ascites, obesity or pleural effusions. (4) Platypnea (dyspnea that worsens in the upright position) is a rare complaint associated with arteriovenous malformations at the lung bases or with hepatopulmonary syndrome, resulting in increased shunting and hypoxemia in the upright position (orthodeoxia). (5) Trepopnea is dyspnea caused by lying on one side. Typically, it results from a disease in one lung or a main bronchus. Lying on the side of the diseased lung results in greater perfusion to the diseased side, leading to a ventilation-perfusion mismatch and resultant dyspnea. It may also be experienced in congestive heart failure where patients prefer to lie on their right in order to allow better venous return. (6) Episodic dyspnea suggests congestive heart failure, asthma, acute or chronic bronchitis, or recurrent pulmonary emboli. (7) Chronic dyspnea is usually progressive. Symptoms often first appear during exertion; patients learn to limit their activity to accommodate their diminished pulmonary reserve until dyspnea occurs with minimal activity or at rest. The most common causes of chronic dyspnea are asthma, chronic obstructive lung disease, ILD, heart failure and cardiomyopathy, but deconditioning is often a major contributing factor in patients with chronic lung disease.

The initial evaluation following the history and physical examination should include a complete blood count (to exclude anemia as a contributing factor to dyspnea), renal function test, chest radiograph, standard spirometry, and noninvasive oximetry during ambulation at a normal pace, also measuring distance achieved over 6 min. The chest radiography may provide evidence of hyperinflation and bullous disease suggestive of obstructive lung disease, or change in interstitial markings consistent with inflammation or interstitial fluid. Abnormalities of heart size or shape may indicate valvular heart disease (e.g. the straightening of the left heart border seen in mitral stenosis) or other cardiac dysfunction (e.g. bottle-shaped heart seen in pericardial effusion). Standard spirometry can distinguish patients with restrictive pulmonary disease from those with obstructive airway disease. However, careful interpretation of the spirometry is required, correlating the numbers with the clinical picture, as a “restrictive lung function” defect may also be seen in morbid obesity or chest wall deformities as well as with interstitial lung diseases. Lung volume measurements and diffusion capacity measurements are generally carried out in patients in whom ILD is being considered, in those who have significant declines in oxygen saturation with exercise, or in those for whom there is a suspicion of ventilatory muscle weakness. Computed tomography (CT) of the chest is valuable in two circumstances—when a patient has crackles on physical examination or reduced lung volumes on pulmonary function test even if the radiography is normal, and for those who have oxygen desaturation with exercise and a low diffusing capacity (occult emphysema). When radiology or lung function testing does not reveal any cause of dyspnea, cardiac disease should be sought. Echocardiography is reserved for patients in whom chest radiography reveals the heart to be enlarged, or in whom the diagnosis of chronic thromboembolic disease or, when there is no other sign of pulmonary or cardiac disease apparent, pulmonary hypertension is being considered. Cardiopulmonary exercise testing is recommended if the etiology of a patient’s dyspnea remains unclear after the initial evaluation described above. This test allows one to determine if the patient’s dyspnea is more likely due to cardiovascular or respiratory system abnormalities, or if it is due to deconditioning.

Which of the following respiratory patterns are characterized by alternating periods of deep and shallow breathing due to fluctuations in co2 levels?

What is the most common cause of pulmonary edema?

Which factor contributes to the production of mucous associated with chronic bronchitis?

Which condition involves an abnormally enlarged gas exchange system?